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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old September 22nd, 2019, 10:30   #1
intro
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Default Chasing after cause of P0302 for weeks, now getting P0030 & P0135

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.

Last edited by intro; September 22nd, 2019 at 10:35.
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Old September 22nd, 2019, 14:32   #2
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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...

Last edited by intro; September 22nd, 2019 at 18:54.
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Old September 22nd, 2019, 18:15   #3
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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.
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Old September 22nd, 2019, 18:58   #4
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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.

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Old September 23rd, 2019, 06:28   #5
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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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Last edited by oilhammer; September 23rd, 2019 at 06:33.
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Old September 23rd, 2019, 08:32   #6
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Quote:
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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.
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Old September 23rd, 2019, 09:10   #7
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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.
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Old September 23rd, 2019, 09:53   #8
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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.
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Old September 23rd, 2019, 10:23   #9
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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.
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Old September 27th, 2019, 06:51   #10
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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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Old September 27th, 2019, 07:25   #11
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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.
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Old October 8th, 2019, 17:11   #12
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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.

Last edited by intro; October 8th, 2019 at 19:53.
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Old October 8th, 2019, 18:35   #13
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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.
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Old October 9th, 2019, 04:50   #14
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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.
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Old October 9th, 2019, 05:11   #15
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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.

Last edited by intro; October 9th, 2019 at 05:14.
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