Chasing after cause of P0302 for weeks, now getting P0030 & P0135

intro

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Hey guys,

I'm losing my mind trying to figure this out, tried posting on Vortex because I have an AZG in my wagon but I don't think that forum is as active and I know there are a lot of knowledgeable folks on here.

I'll try to make this is brief as possible.

Car sat for like 7 months waiting for some work that I finally got to this summer. Replaced my exhaust manifold, valve cover gasket, did a complete timing belt job, crank seal, ignition wires, battery, new muffler, intermediate pipe clamp.

- I'm 99% positive I didn't mess up the timing belt job. Had everything correct and at TDC. It wasn't my first rodeo.
- Upon 1st start-up, car shook and bucked, smoked (I had my ignition wires incorrectly routed to the coil pack and had a vac line unplugged. I also think it's possible some of the Slip Plate I had used to restore the manifold burned off?)
-Things smoothed out a bit after that but I am still regularly getting a flashing CEL that will sometimes stay and sometimes go on its own-2nd. cylinder misfire. Heavy smell of fuel. Detonation in the exhaust.
-The misfire was present last winter before the car was parked, only when accelerating uphill, without wet conditions being necessary, so I always assumed my old ignition wires were the culprit. It didn't happen consistently enough at that point to care.


Things I have tried:

-Swapping out the coil pack-no improvement
-Replacing my plugs-no improvement
-Unplugging the connector on the large air intake hose (not MAF)-SLIGHT improvement
-Added some Techron to my tank (which had less than a 1/4 tank these 7 months-wondering about bad gas and moisture building up-will be trying to add fresh gas soon.)-SLIGHT improvement
-Put electrical tape on some suspect vac lines I should probably change.
-Confirming pulse at fuel injectors using "screwdriver trick."

Things I have not tried:

-Compression Test
-Actual testing of spray pattern fuel injector #2 (have never done this kind of test)
-Replacing all vac lines, which are the stock lines. There is a hose that goes into the larger air intake hose (under that plug I had tried disconnecting) and when I manipulate it where it connects to the nozzle I hear a hiss. Inspected it and it checked out ok, but maybe the clamp has loosened up?

Unfortunately, yesterday I was at one point able to get a smooth idle for quite a bit of time and kept revving the motor up to like 4K RPMS to see if it would miss. It didn't but then when I restarted the car I had the same misfire code plus 2 NEW ones-P0030 and P0135. I then noticed my pre-cat 02 sensor wiring was resting on the heat shield. I had forgotten to route it away after all the work and this was the first time the car got up to running temperature. There is no melting in the wires. Possible all this testing of the car ruined it? It is the original sensor that I removed for the first time ever doing the exhaust work. I fear the catalytic is next.

Any advice much appreciated. Really hoping it's not a compression issue. Car has 177K on it.
 
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intro

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Little update.

I decided to start the car and let it idle for a while, just in case it was a dirty injector, I could allow the Techron to do its thing. Sure enough, the misfire went away as time went on. I'd step in every once in a while over the course of 25-30 minutes and give it gas without any hesitation or sputtering. If however, I shut the car off and started it again, I would still get those new pre-cat 02 sensor codes-p0030 & p0135. The last time I cleared the codes, I tried restarting the car and then found that my battery was dead, so yet another problem to diagnose. To think I used to enjoy troubleshooting and working on cars-Haha. Jeez.

Since I'm not seeing any issues with the wiring on the 02 sensor maybe it's time for a new one. I'm not going to stress on whether the constant misfires killed it while I investigate. I usually go with the Ford Bosch 4-wire available from the box stores for the post-cat because it's cheaper. Is there a similar option for the front sensor? I'm seeing more than 4 wires on this one. EDIT: GUESS IT'S THE BOSCH WIDEBAND 17351 I'LL NEED, CAN'T SEEM TO GO CHEAPO FORD ALTERNATIVE.

Next time I start the car after getting the battery charged and the 02 sensor swapped I'll have a little more information as to whether the misfire is a cold-start issue or not but I'm feeling a bit more at ease now that it's not a catastrophic problem I'm dealing with. I'll probably order the vac lines kit from IDParts as well.

Open to suggestions...
 
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intro

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I think the battery discharged because the terminals weren't tightened down. Didn't know that happened but it makes sense. I've been taking out the battery and putting it back in so often I must have forgotten to tighten the terminals.
 

WildChild80

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Glad you have made progress, I had a 2 liter Jetta for a few months and eventually traded it for a TDI new beetle, the Jetta had lived a hard life and was in rough shape.

As for the O2 sensor, no idea but if it's got more than 4 wires, it's a wideband and wideband usually means wide cost or high cost...it'd be worth a shot to pull some from the salvage yard and tuck them in your bag...stuff like that I try not to pay for because I don't expect it to work anyway.

Sent from my Pixel XL using Tapatalk
 

oilhammer

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There are just too many to list....
You need to use a Bosch oxygen sensor, and you need to make sure it is the correct one (as there are many two liter VAG gas engines, they often get sourced incorrectly, and they are not all the same).

The AZG uses the POST-catalyst sensor for fuel trim (as do most modern gas engines using wide band type sensors). It allows for better catalyst function. However, non-EOM catalysts on these engines really cause some havoc with the lambda control. But the 135 DTC is just for the heater. However I have seen shorted heaters take out that circuit in the ECU, both front or rear.

The Bosch short number for the front sensor is 17-351 and it is the same type kit that the dealer will sell you (06A-906-262-BC). They are available in the aftermarket for usually around $115 or so.

These engines are also very picky about the correct spark plugs. Again, a constant source of miss-informed parts people will sell the incorrect ones. Make sure you have the right ones, I believe they are NGKs, laser platinum single ground. Some of the earlier cars (AEG engine) use a twin ground Bosch plug.
 
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intro

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02 Jetta Wagon
You need to use a Bosch oxygen sensor, and you need to make sure it is the correct one (as there are many two liter VAG gas engines, they often get sourced incorrectly, and they are not all the same).

The AZG uses the POST-catalyst sensor for fuel trim (as do most modern gas engines using wide band type sensors). It allows for better catalyst function. However, non-EOM catalysts on these engines really cause some havoc with the lambda control. But the 135 DTC is just for the heater. However I have seen shorted heaters take out that circuit in the ECU, both front or rear.

The Bosch short number for the front sensor is 17-351 and it is the same type kit that the dealer will sell you (06A-906-262-BC). They are available in the aftermarket for usually around $115 or so.

These engines are also very picky about the correct spark plugs. Again, a constant source of miss-informed parts people will sell the incorrect ones. Make sure you have the right ones, I believe they are NGKs, laser platinum single ground. Some of the earlier cars (AEG engine) use a twin ground Bosch plug.
I do have the correct Laser Platinum plugs (NGK (7968) PZFR5D-11.) Thanks Oilhammer! I had determined 17351 was the correct sensor, found a source for around $75 last night, so will probably order it. Now you have me concerned it could be an issue with the ECU (hope not.) What do you think is the likelihood this happened because the wires were hanging on the heat shield? I guess it could just be a coincidence. Like I said, I see no melted wires.
 

oilhammer

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There are just too many to list....
I'd check to make sure all the fuses are good, but both sensors' heaters are powered by the same circuit, along with some other items (I think the MAF, and maybe the PCV heater if equipped). So if the fuse was blown you'd have other DTCs.

The heaters' power is always on when the key is in the run position, but the ground is pulsed via the ECU, so that is why a shorted heater *can* cause that circuit inside the ECU to fail.
 

intro

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I'd check to make sure all the fuses are good, but both sensors' heaters are powered by the same circuit, along with some other items (I think the MAF, and maybe the PCV heater if equipped). So if the fuse was blown you'd have other DTCs.
The heaters' power is always on when the key is in the run position, but the ground is pulsed via the ECU, so that is why a shorted heater *can* cause that circuit inside the ECU to fail.
Yeah, I had checked out the 2 related fused yesterday-No dice.

Will try swapping the 02 sensor first and go from there. Would you know if this sensor requires splicing or does the connector included work? Thanks again.
 

oilhammer

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There is no splicing, it is plug 'n play. The wire will be longer usually, so you may have to use the included zip ties to secure it.
 

intro

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There is no splicing, it is plug 'n play. The wire will be longer usually, so you may have to use the included zip ties to secure it.
That was easy, and I finally learned where the 2 harness connectors live under the black box. 02 sensor code has cleared up. I am still getting a slight misfire and am wondering whether the area in the picture is suspect. That's where I am hearing a hissing sound. Anyone have any suggestions? I cleaned the MAF already but I'm not sure what this area is called. I think it's a check valve of some sort correct? I sometimes see oil around the plug and I'm guessing that's just "blow by"? The sound seems to get louder when I mess with the small tube underneath but it has no splits. Sorry if this is AZG specific.







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oilhammer

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That is the PCV heater. Spray some carb spray around that area with the engine running, while watching the lambda correction on the scan tool. If it spikes when you spray, you know you have a false air leak there, and you need to fix it.
 

intro

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That is the PCV heater. Spray some carb spray around that area with the engine running, while watching the lambda correction on the scan tool. If it spikes when you spray, you know you have a false air leak there, and you need to fix it.
Oilhammer, I could use some of your know-how. This is getting really nuts. Still getting misfires, multiple ones now while test driving. The p0300 reared its head again even though I had swapped out the old 02 sensor and eliminated it. Not sure where to look next or if it's time to finally spring for a legit VAG cable. Chasing after some electrical gremlins as well which is making things tougher, either that or I've got a draw somewhere. I suspect it's the alternator because the battery is draining after driving or running the car, or the wiring, but I'm not getting an alternator light. My plan was to drive to Advance and have the charging system tested but alas, as I was letting the car warm up a bit today, I lost all throttle response. Would press the pedal and at first I felt a little sputtering, then it went back to idling, then zero throttle response, then the car sputtered and died. Of course I haven't been able to test it again because now I have to go get the battery charged. Could this be the fuel pump that's been giving me problems all along? It feels reminiscent of the days when I had rust in my Scirocco's pump. Guess I'll be removing the back seat cushion and checking back there, or is it possibly the throttle position sensor? That wouldn't explain the car sputtering out though. Two other oddities, I had an airbag light and a flashing key light in the cluster for the first time ever. Air bag light shut off on its own, flashing key went away once I stepped outside and manually armed the alarm at the lockset.
 
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intro

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Also saw a mouse crawl out of the rain tray the other day on start-up. I see the beginnings of a nest but I'm praying the ECU wires didn't become lunch. Going to take a look tomorrow. All these problems happening all at once seems suspicious.
 

oilhammer

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If the charging system is not working correctly, the engine management system cannot work correctly. Computers do not like to work below about 9.6v. The battery normally drops to about 10.5v (from a static 12.6v) during startup. But running, it is technically a 14v system (see the tag on the alternator). So everything is really designed to work on 14v, including the ignition coil, fuel pump, and throttle motor.

So get that working, you may find much of your problems go away.
 

intro

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If the charging system is not working correctly, the engine management system cannot work correctly. Computers do not like to work below about 9.6v. The battery normally drops to about 10.5v (from a static 12.6v) during startup. But running, it is technically a 14v system (see the tag on the alternator). So everything is really designed to work on 14v, including the ignition coil, fuel pump, and throttle motor.
So get that working, you may find much of your problems go away.
Thank you. I've dealt with plenty of flat batteries and dead alternators before and never had that happen. In the past when troubleshooting, I've never had to worry about the car once it was running though. I'd hate to get stranded with an unresponsive accelerator pedal. I guess I could just use my voltmeter and look for that dip with the engine running.

If it is the alternator, which was replaced about 4-5 years ago (about 30k miles or so), is it possible to replace just the voltage regulator? I had learned to do this on our Passat and it was a good deal less expensive.
 
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oilhammer

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Was it a Bosch reman alternator that was installed? If not, then I would get the whole thing. If it was, then it may not be the problem, but in my experience, my charging system diagnostics are pretty quick once I open the hood and see a non-OEM unit there.

However, you can check the harness to the alternator for bad connections. It plugs into the car on a holder above the starter (the small wires...two go to the alternator, two go to the compressor), and the large wire goes straight to the fuse link box above the battery, on the far left as looking down on it from the front. Those fuse link boxes often melt, too, especially if the battery will not take a charge.
 

intro

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Was it a Bosch reman alternator that was installed? If not, then I would get the whole thing. If it was, then it may not be the problem, but in my experience, my charging system diagnostics are pretty quick once I open the hood and see a non-OEM unit there.
However, you can check the harness to the alternator for bad connections. It plugs into the car on a holder above the starter (the small wires...two go to the alternator, two go to the compressor), and the large wire goes straight to the fuse link box above the battery, on the far left as looking down on it from the front. Those fuse link boxes often melt, too, especially if the battery will not take a charge.
Haha. It was whatever German Auto Parts was selling at the time, I believe a Bosch. I checked the connection at the alternator itself and where the fuseable links are but I haven't checked in that area above the starter. I remember what a nightmare it was sorting out a charging issue on our b4 Passat TDI. It took me a month to realize that the connector at the alternator was not fully seating. In that case I was getting an alternator charge light. Also got one when I changed it on this car. Strange I'm not getting one now. Thanks Oilhammer. I'm going to get the multimeter and do some reading once the battery is boosted.
 
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wonneber

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If it is the alternator, which was replaced about 4-5 years ago (about 30k miles or so), is it possible to replace just the voltage regulator? I had learned to do this on our Passat and it was a good deal less expensive.
If the regulator is bad it can be replaced.
Probably similar to the Passat.

Maybe measure for AC voltage with the car running and lights and AC on.
I would not want to see much but it would indicate a bad diode.
 

oilhammer

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You really need a proper scan tool first. Although at least the basics of the charging system can be checked with a volt meter. You do not need to go anywhere for this. Even a cheap volt meter will work. It is either charging or it isn't (most likely, that is usually how Bosch alternators work).

If you turn the key ON, the battery light should come on. If it does not, you may have a field wire problem (the above mentioned harness that plugs in atop the starter) or the alternator itself.

You need a gauge to check the fuel pressure, but again, like the alternator, my experience is usually the pumps work or they don't. There is a fuel pump relay, 409 I think, located inside the car. Provided your door latch microswitches are working correctly, that car should briefly energize the fuel pump when you open the driver's door. If you listen carefully you can usually hear it click back off after a second or so.

Those relays sometimes fail. But again, they usually fail and stay failed, or may begin to work again after the car sits. They do not fail "half on".

If the car has been sitting, you could have some varnish from old gas getting stuck in the fuel filter, as well as the injectors, especially if it is the returnless system (not sure which your specific car uses).

If the battery is fully charged, and can maintain at least 11v or so with the car running even with a bad alternator, the car should run just fine for a little while at least.

I think you likely have several problems, might be related, might not. But best to try and address them individually at first. Since the charging system is important, and isn't directly tied into the engine management for proper function in terms of allowing the engine to run, and it is fairly simple, I'd go after that first.
 

intro

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Picked up the battery from Interstate. I dropped it off at 10 and picked it up at 4. Not sure what time they put it on the charger but when I went to pick it up the knowledgeable guy from inside the warehouse had left for the day and the young kid at the counter went and got it. Put the voltmeter to it and said "12.2- fully charged." Ummm, I debated that it should be 12.8 but he said I'd be able to start the car. He offered to keep it on the charger overnight which is how I've normally done it I think but I wanted to get home and check the charging system. After starting the car I was down at 11.8. With headlights, radio, HVAC, garmin, dome light, and hazards on, it dipped down to 11.3, and when I shut all those off again but left the car running, I was now at 11.5. Clearly, I have a charging issue. Wiring and plugs looked ok. Haven't tried cleaning up grounds. Battery indicator bulb lights up on ignition turn. Pretty disappointed if a new Bosch has given up after only 3.5 years. The good news: the throttle has come back and I'm not getting any new, random warning lights. I'll probably pull the alternator and have it bench tested just to rule it out.
 

intro

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You really need a proper scan tool first. Although at least the basics of the charging system can be checked with a volt meter. You do not need to go anywhere for this. Even a cheap volt meter will work. It is either charging or it isn't (most likely, that is usually how Bosch alternators work).
If you turn the key ON, the battery light should come on. If it does not, you may have a field wire problem (the above mentioned harness that plugs in atop the starter) or the alternator itself.
You need a gauge to check the fuel pressure, but again, like the alternator, my experience is usually the pumps work or they don't. There is a fuel pump relay, 409 I think, located inside the car. Provided your door latch microswitches are working correctly, that car should briefly energize the fuel pump when you open the driver's door. If you listen carefully you can usually hear it click back off after a second or so.
Those relays sometimes fail. But again, they usually fail and stay failed, or may begin to work again after the car sits. They do not fail "half on".
If the car has been sitting, you could have some varnish from old gas getting stuck in the fuel filter, as well as the injectors, especially if it is the returnless system (not sure which your specific car uses).
If the battery is fully charged, and can maintain at least 11v or so with the car running even with a bad alternator, the car should run just fine for a little while at least.
I think you likely have several problems, might be related, might not. But best to try and address them individually at first. Since the charging system is important, and isn't directly tied into the engine management for proper function in terms of allowing the engine to run, and it is fairly simple, I'd go after that first.
Ok, so...
-Found an old post referencing the blue wire (exciter?) in that wire harness above the starter. No wires appear frayed or damaged.
-Cleaned up positive cable connections on battery.
-Took the alternator out and had it bench-tested at Advance. Got these results:

-Have not had any noise from the pulley or seizing. Stuck a screwdriver in the alternator blades and the pulley spins counter-clockwise but not clockwise.
-Removed the voltage regulator and it seems fine to me. The brushes seem to have enough "meat" on them:

-Could there be some other internal failure I'm not aware of. Since I bought the alternator the terminals have felt wiggly but GAP had assured me it was fine when they tighten down, which is true. It's never been an issue before. Pretty dumbfounded at this point.
 
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intro

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Looks to me like you need a new alternator.
The whole thing, yeah? I wonder why the warning light wasn't coming on? Confirmed the bulb is good. I guess I'll have to trace that wire all the way to the cluster. I think I'm just going to install some gauges, so I'll get to the bottom of it somehow.
 
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intro

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Looks to me like you need a new alternator.
New alternator in, charging again, still multiple misfires pending though. :/

I'm suspecting this is a vac leak so Ill try checking there next. Maybe replace the vac lines which have never been done.
 
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oilhammer

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OK, so you got one problem fixed. Moving on to the next, if you suspect a lean misfire condition, I would use a scan tool and look at fuel trim (lambda). It should hover around 0 once the engine is warmed up some. Usually within about 5 minutes it should be in closed loop and lambda control.

There are hardly any vacuum lines on that engine. It is super simple. You can also watch the misfire counter with a scan tool to see which cylinders specifically are misfiring and when.
 

intro

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OK, so you got one problem fixed. Moving on to the next, if you suspect a lean misfire condition, I would use a scan tool and look at fuel trim (lambda). It should hover around 0 once the engine is warmed up some. Usually within about 5 minutes it should be in closed loop and lambda control.
There are hardly any vacuum lines on that engine. It is super simple. You can also watch the misfire counter with a scan tool to see which cylinders specifically are misfiring and when.

Thanks. Yeah, I just realized there are not a lot. It looks like one was replaced on the left side. The other 2 over by the driver's side are still that corrugated style.

I'm going to need to get a VAG cable and the software, it's time.

This will seem like a stupid question, but I have the ignition wires going left to right 1-4 on the cylinder head and then according to the letter order on the coilpack. Does that sound right to you?

I'm also wondering if the NGK wires I picked up from Amazon warehouse were bad and thus returned. You can test wires for resistance right?

The misfire has gotten worse I think over the last 2 weeks. It used to be just p0302, now I'm getting P0300, p0302, p0304(P).

Anyway, I can only keep guessing so I'm ordering the Rosstech now.
 
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oilhammer

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Ignition wires in the aftermarket, much like spark plugs, are often sold incorrectly for the 2.0L engines.

The AEG uses 06A-905-409-L, the AZG, AVH, BEV use 06A-905-409-N.

I would only use OEM type (Beru is usually a good brand) wire sets, and they really can only fit one way. They come already laced in such a way as to be pretty darn impossible to put on the coil incorrectly.
 

intro

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Ignition wires in the aftermarket, much like spark plugs, are often sold incorrectly for the 2.0L engines.
The AEG uses 06A-905-409-L, the AZG, AVH, BEV use 06A-905-409-N.
I would only use OEM type (Beru is usually a good brand) wire sets, and they really can only fit one way. They come already laced in such a way as to be pretty darn impossible to put on the coil incorrectly.
It's funny, I went and checked out the Amazon page for the wires and now I'm seeing a whole bunch of reviews saying they caused misfires. I guess I only read one and didn't dig deep enough. I think you're onto something Oilhammer.
I went out hoping to try switching the wires 2 and 3 as some people said they arrived mislabeled and it affected performance (not clear on how the length would affect that). Didn't do anything but the question prompted me to check what I had in there before that worked just fine (NGK Part #: NGK 57021). The Amazon Part # is NGK RC-VWC039. I'm hopeful this will straighten me out but I do have my VCDS cable on the way just in case.

EDIT: NGK 57021 and VWC039 are the same thing. Damn!
 
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intro

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I'm going to hope that new wires will do the trick, but I will probably read the ohms on those NGK wires first, before ordering tomorrow. I'm sure the OEM wires at the dealership would be an arm and a leg.
One thing I continue to see, is the misfire gets better as the motor warms up. On cold start I will have 300, 302, and a (P)304. After warming up I can have the car revving, and only when the I ease off the gas do I start seeing the flashing CEL. I tried the poor man's version of VAG-com and scanned when I was revving the engine-No codes, as soon as I eased off I'd get P0302(P).
 
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