Narrowing down low power causes

Have you confirmed how much vacuum your vacuum pump is making at idle and at 2000 RPM?

You definitely need new gaskets if removing the intake manifold. They crush to seal.


I saw someone in the Passat section use engine oil dye to find a leak in his intercooler
https://www.napaonline.com/en/p/BK_7652661


Some amount of leakage is normal in the charge air system. What you will want to do it clean all the connections well (brake clean works great) and then go for a drive and see how much oil is coming out. You'll know if you have a big leak by how quickly a connection gets oily.

I don't have any specs for the TDI but on a transport truck, most are allowed to loose 5-7psi of pressure over 10 seconds at around 30 psi charge through the intercooler.

wonneber said:

2000alhVW said:

Question: when removing the I/M, do I need new gaskets? Or is it okay to re-use the old ones?[/B]

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New gasket.
I could have reused mine as it came off intact but did not want to take a chance.
Also, you should replace the o-ring between the EGR valve and the manifold.

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Yep. I found this to be pretty spot on when I dove in last night.

burn_your_money said:

Have you confirmed how much vacuum your vacuum pump is making at idle and at 2000 RPM?
You definitely need new gaskets if removing the intake manifold. They crush to seal.
I saw someone in the Passat section use engine oil dye to find a leak in his intercooler
https://www.napaonline.com/en/p/BK_7652661
Some amount of leakage is normal in the charge air system. What you will want to do it clean all the connections well (brake clean works great) and then go for a drive and see how much oil is coming out. You'll know if you have a big leak by how quickly a connection gets oily.
I don't have any specs for the TDI but on a transport truck, most are allowed to loose 5-7psi of pressure over 10 seconds at around 30 psi charge through the intercooler.

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I've confirmed it makes vacuum at idle. Not 2000 rpm. I should have someone rev it to 2,000 while in Park, under no load?

I went to town removing my intake manifold to check for clogs. Mixed results. EGR system was surprisingly clean. The EGR valve and piping looks much newer than expected.
Once I removed the EGR, I could see the I/M is a bit worse than previously thought, but still not awful like ones I've seen here.
I got a few I/M bolts off easily, but one of them was completely insane. I realized the project was hopeless without a bolt extractor and new I/M bolts. So I put the car back together.
From these pictures, do you think it's prudent to go back and finish the job?






In my ignorant opinion, the I/M looks much worse in pictures than it actually is. There is really only a thick coating on the walls, but not much more. When scraping it off with a slotted screwdriver, there isn't much depth.

There was a post where they were having low power and cleaned there intake and still had issues. They then pulled the intake again and found the runners were clogged were they could not see. If I remember correctly they cleaned by scraping the carbon out the first time. I believe they ended up cleaning it the second time by burning it our.

Sorry I can't remember the post to reference for you.

When I had a intake bolt that the hex stripped out of I used these type of bolt outs. Hammer it on to the bolt head and used a ratchet to remove. The harder you turn he deeper they bite the bolt.

https://www.lowes.com/pd/IRWIN-BOLT...w0UvbMURMaSTwBUAwvsk5lvARMsrzZ-EaAuvEEALw_wcB

Hyde7278 said:

When I had a intake bolt that the hex stripped out of I used these type of bolt outs. Hammer it on to the bolt head and used a ratchet to remove. The harder you turn he deeper they bite the bolt.

https://www.lowes.com/pd/IRWIN-BOLT...w0UvbMURMaSTwBUAwvsk5lvARMsrzZ-EaAuvEEALw_wcB

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Awesome! Thanks for the link. Yep, I think I'll finally have to buy a set of those Irwins after seeing them linked on various forums for the past 8 years or so. Good thing I have 2 Lowe's within 4 miles of me!

I'm feeling somewhat optimistic of cleaning the intake. At the least, it will just rule another thing out.

Search for intake cleaning methods. There a process of using compressed air and a propane torch to burn he carbon out. Sure there are some YouTube videos also

No access to compressed air. I thought of ideas, from using a box fan on high to buying 'canned air' only to realize it ain't oxygen in those cans.
I spent 30 minutes calling machine shops all over town. About 10 of them said "we don't do auto work. Insurance reasons."

Anyway...I did all that work to find this...



Will clean it out, and onto the next possibility I guess.

I did 45mins of diagnostic highway driving. Not sure what to make of it.
Starting my 200 mile trip, the car was so dangerously slow that I unplugged the MAF 10 mins in. For the first time ever, unplugging the MAF transformed it into a different car. Like if you bought the V6 instead of the 4cyl model. BUT still huge lack of power. The difference was I could start a hill at 70 and slowly creep down to 50 (pedal floored), rather than starting it at 65 and be lucky to maintain 35mph.
On flat ground or a slight downhill, the car felt pretty good. I got it up to ~95mph a couple times.

I drove it around town and it was back to gutless. I noticed a few things. For the first time, I noticed black smoke. Just a little bit of "wheezing" after recently started up. It will have some power, and upon heavy throttle it will smoke for ~1 min until power is cut again. No smoke on start up, only smoke under throttle after an off/on reset

I put ~250 miles on the car since Sunday. It had CEL for MAF, obviously, and had logged P1556 again. It has triggered this before, but takes ~50+ miles.
I did diagnostic runs on the highway. It seems like the car might actually be very momentarily over-boosting, and the ECU trips limp mode with out a CEL or any hard evidence.
I logged actual vs requested boost, and, after some tinkering, could actually get it to hit and maintain 1900-2100 mbar for some significant time.
What's funny is, I tried to trigger the limp mode thing again and I couldn't. Super weird. Been battling this relentless demon for 10 months non-stop, and suddenly I can't find it.
I even plugged the MAF (which historically never registered more than ~450 kg/min) back in and it was actually reporting into the mid-700s. I did some "spirited" driving through mountain back roads and it almost pushed me into the seat.

It still feels restrained though. Going to upload logs.
My new theory is it builds boost in a gear, then overboots upon shifting and computer trips limp mode.

Also, any thoughts on this?

I plan on adjusting the start of injection timing via the IP, but how bad is this? It is just barely inside the upper limit. Would this contribute to any issues?

Graph of requested vs actual boost while in limp mode.


Pedal floored. This pretty obviously confirms the computer is intentionally cutting fuel, no?

The intake doesn't look to bad but can be restricted in the intake where you can see it. In the tread I referenced the OP cleaned his intake (manually) with a scraper and screwdriver and wasn't able to get down into the intake where you cant see and thought it was nice and clean. And still had the same problem. Then he cleaned it by burning it out and finally fixed it.

I wouldn't dismiss a clogged intake just yet.

Also when you had the intake off did you use a mirror and check the intake ports in the head to make sure there not clogged up?

The clogging you see is excessive and will definitely contribute to, even cause your issue.

I also want you to remove the turbo and look it over really good.

I bet you have the classic compound effect of the turbo clogging and getting sticky, while the intake is restricted causing limp mode due to overboost caused by a sticky actuator and veins.


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I will check but I think I have a manifold that I can clean for you and ship to you. All I'd ask is for you to pay shipping and send me yours when you swap it out.

I will check in the morning to see if I still have it.

Hyde7278 said:

The intake doesn't look to bad but can be restricted in the intake where you can see it. In the tread I referenced the OP cleaned his intake (manually) with a scraper and screwdriver and wasn't able to get down into the intake where you cant see and thought it was nice and clean. And still had the same problem. Then he cleaned it by burning it out and finally fixed it.

I wouldn't dismiss a clogged intake just yet.

Also when you had the intake off did you use a mirror and check the intake ports in the head to make sure there not clogged up?

Click to expand...

Got the manifold off last night. I filled the intake with some of that foamy engine cleaner and left it. I did the cleaning portion today. I bought some cheap hook & pick set from Walmart (IMMEDIATELY fell apart lol) and started to manually scoop the goop out. I thought it was endless because it's so pasty. Then I tried a propane torch in combination with a box fan on high. Definitely not ideal, but I got a pretty decent burn going on after a while. After that, I spent a while scraping out the charred goop. It does look a lot better, but not as confidently clean as a tank'd, baked and blasted one.

I still have the manifold off the car, and I'm definitely going to check the intake ports more thoroughly. I tried to use my phone camera to see them, but wasn't very clear. Nothing looks too out of shape though.

eddieleephd said:

The clogging you see is excessive and will definitely contribute to, even cause your issue.

I also want you to remove the turbo and look it over really good.

I bet you have the classic compound effect of the turbo clogging and getting sticky, while the intake is restricted causing limp mode due to overboost caused by a sticky actuator and veins.

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I was tempted to remove the turbo, but I just can't commit to that right now. I want to at least try to be proper with buying new gaskets, and I can't get them in time to drive home tomorrow.

Hyde7278 said:

I will check but I think I have a manifold that I can clean for you and ship to you. All I'd ask is for you to pay shipping and send me yours when you swap it out.

I will check in the morning to see if I still have it.

Click to expand...

Wow. that would be awesome.


I cleaned my EGR valve as well, which was arguably in worse condition on the backside

Copper nuts as well, guess that's a job for next time you have the intake off.

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eddieleephd said:

Copper nuts as well, guess that's a job for next time you have the head off.

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Yes, copper nuts too. You mean 'next time I have the manifold off," no?

Also, what all clogs up on the exhaust side? I know about the turbo vanes getting sticky, but I've also read something about downpipe clogging up with goop as well? Or the cat being clogged?

Yes, I do, edited
Sometimes I get ahead of myself, I often edit after re-reading
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My car goes into limp mode from over boost also. When it happens it doesn't trip a check engine light. Mostly happens to me on the highway. When it happens I can tell by the lack of power and the sound of the exhaust (gets louder and deeper)

What I do is I push in the clutch and shut the car off and then restart it and release the clutch. By shutting it off and restarting it resets the limp mode.

My overboost is doused by sticking vanes in the turbo. I will replace the turbo one I get the suspension all set. But I might use oven cleaner to clean the vanes in the mean time.

Hopefully the cleaning you have done will help and I will see if I can find the manifold for you.

Hyde7278 said:

My car goes into limp mode from over boost also. When it happens it doesn't trip a check engine light. Mostly happens to me on the highway. When it happens I can tell by the lack of power and the sound of the exhaust (gets louder and deeper)

What I do is I push in the clutch and shut the car off and then restart it and release the clutch. By shutting it off and restarting it resets the limp mode.

My overboost is doused by sticking vanes in the turbo. I will replace the turbo one I get the suspension all set. But I might use oven cleaner to clean the vanes in the mean time.

Hopefully the cleaning you have done will help and I will see if I can find the manifold for you.

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When I had to key cycle for the exact reason, I got to where I'd just switch the key off without pushing the clutch in, just a quick blip does the trick. I was 400 or so miles into a 1200 mile trip when I realized there was a problem and in the summer from Virginia to Arkansas through the southern states without AC...

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I shut my car off while moving and it came back to life simply by switching the key back to "on". It almost acted like a manual transmission car, where you leave it in gear, and simply flip the key to on - no starter motor necessary since the engine is already turning.

My auto did the exact same thing! Unless I'm mistaken and it never stopped turning...

2000alhVW said:

Yes, copper nuts too. You mean 'next time I have the manifold off," no?
Also, what all clogs up on the exhaust side? I know about the turbo vanes getting sticky, but I've also read something about downpipe clogging up with goop as well? Or the cat being clogged?

Click to expand...

The filter in the cat has been known to clog up.

When you clean the port in the head you -MUST- have the valves closed.
You do not want any bits falling into the chamber.
Easiest way might be take the valve cover off and crank the engine from the crank pulley (never the cam or pump) until the 2 cam lobes for the cylinder you will be cleaning are both up.

You have the bumper cover off, pop the intercooler off and test it. Cover 1 hole and blow in the other one. If it leaks, get it welded. Be sure to get the tube and clamp that goes to the intake back on right or it will pop off and rub against the power steering and then you'll have another leak.

wonneber said:

The filter in the cat has been known to clog up.

When you clean the port in the head you -MUST- have the valves closed.
You do not want any bits falling into the chamber.
Easiest way might be take the valve cover off and crank the engine from the crank pulley (never the cam or pump) until the 2 cam lobes for the cylinder you will be cleaning are both up.

Click to expand...

Plus one for ensuring the valves are closed...

I've cleaned the intake ports and got gunk under the valves and it wouldn't make compression for a while, I learned the hard way and finally got it fired up...



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I did not do any port cleaning.
This is how all 4 of my ports looked:

Looks good to me. Nothing accumulated on my picks. I put it back together.
Zero change. Fun learning wrenching on and learning about this motor, but by god is that a filthy job.

Did research and more tinkering. At idle, testing an open vac line shoots the needle up to 25+ inHg. Checked with 2 MityVac hand pumps. Same.
I tested open vac at idle while jiggling (all the way to the brake booster) the hose from vac pump. No change.
Observed actuator on start up. It moves.
https://i.imgur.com/NWSvyQ2l.mp4

I've tried to outsmart the ECU regarding limp mode. Accelerate extremely slowly up to ~60, then ask for power. Sometimes it complies.
I've tried driving --> limp mode. Shut off --> restart. Floor it. Spins tires in first gear, but power is cut within 2sec.
I've tried key off, key on, in neutral at highway speeds, to try to get boost back while staying in 4th gear. Sometimes that works.
I used a trick from Canadian Grizzly's Limp Mode thread. Actuator vac line directly to the brake booster T. His post says "You'll get an EGR code, but your turbo oughta work great."
I actually found the opposite. My car ran the worst I've ever seen it. Like limp mode in limp mode. Stopped. Put in park. Key off. wait 30 sec. Key on. Gave it throttle, literally went into limp mode within .2 seconds, the quickest I've ever seen it. I am not exaggerating.
This computer seems extremely sensitive to overboost. And will kick into limp mode at a feather's touch. I don't see how anyone could drive with the actuator connected to the vac pump T.

Then I did the opposite!
I disconnected the actuator completely. Car drives so much better!! No limp mode!
Previously it went like this

• MAF connected - extremely low power. Like, gonna cause an accident 25mph on the highway.
• MAF unplugged - MUCH better. Slow, but very drivable. Stay in right lane, but you'll be okay
• Occasionally tricking ECU out of limp mode - noticably more power, but extremely easy to kick back into limp mode. A single gear shift or letting off throttle too rapidly.

Drove 20mins going up steep hills that I previously had to ride halfway on the shoulder with my hazards on. It flew up them, maintaining 50mph. The MAF was plugged in for this.

I also tried to clean the turbo. I got lazy and sprayed Easy-Off down the EGR port. I found it near impossible to get the EO to the turbo. Went underneath and sheared a flange stud. Oops...

At this point, I think my actuator rod is out of adjustment. It's so minor, I can't tell if it's true or just eye tricks, or just an inaccurate gauge. VNT moves within 1st hand pump of MityVac. Which shows less than 2inHg on the gauge. Additionally, it seems maxed out right around 16". It also does not retract until 15". I think this would explain everything, but does seem a bit minor. I don't know

About the broken turbo flange stud, what do you think I should do? Order 3 nuts, 3 new studs, and flange gasket? Source stud locally for $1 and buy new nuts?

Replace one and new nuts.
And flange gasket

My honest preferred method is to use a reverse drill bit, left hand, and drill to remove.
Usually comes out with the bit.
Forward drill bits, right hand, tend to drive studs in and force you to extract them.

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eddieleephd said:

My honest preferred method is to use a reverse drill bit, left hand, and drill to remove.
Usually comes out with the bit.
Forward drill bits, right hand, tend to drive studs in and force you to extract them.

Click to expand...

2X on this one.
You have to go 100% straight through the center but it's worked for me in the past.

Did I miss a post about checking the map sensor?


Also, PB blaster is your friend, give it 30 minutes or 2 hours and it'll do wonders for rusted nuts and bolts


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WildChild80 said:

Did I miss a post about checking the map sensor?


Also, PB blaster is your friend, give it 30 minutes or 2 hours and it'll do wonders for rusted nuts and bolts


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Click to expand...

Never ever read anything about checking/testing MAP sensor.

Unplug the MAP and see if it changes anything.
That's the test all together.

2000alhVW said:

Never ever read anything about checking/testing MAP sensor.

Click to expand...

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2000alhVW said:

Never ever read anything about checking/testing MAP sensor.

Click to expand...

Use vcds and see what it's reading, it should be reading what your barometric pressure is and boost on top of that so you'll have to subtract your barometric from total pressure to read how much boost the map is reporting, but you'll also need a manual gauge to verify your map is close to or matching.

If you unplug your MAP it should just go into limp mode, might be wrong but if the ECU doesn't know how much boost it's making it should go into limp mode.

You can unplug your MAF to test but you've already done that.

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eddieleephd said:

Unplug the MAP and see if it changes anything.
That's the test all together.

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Click to expand...

I kinda assume the computer would either freak out and retreat to limp mode, or just go off of a pre-determined middle-of-the-road value such as when the MAF is unplugged and it simply uses 550 for all calculations.

I'll try it.
Also, check out these graphs.



also found EGR setting had been changed. Apparently it's at the max value, per VCDS.
I'm now curious...is VCDS the only way to change this value?

At this point, I think my diagnosis is pointing to the turbo being gummed up.
I paid much closer attention to the actuator. At first, I thought the rod was out of adjustment.
I went to go adjust the rod, and found something odd. When I was testing the actuator in the past, I would hook up a hand vacuum pump. It would hold 22+ "hg, no issue. And I would press the release valve on the vacuum pump, which relieves vacuum moderately rapidly. The actuator would retract smoothly. No jumps, or catches.
BUT
This time, I couldn't get a good connection, so it was leaking vacuum at one of the fittings. I pumped it up to ~20, and then I let it slowly leak vacuum. Under very slow vacuum removal, the actuator did not retract! It stayed pegged at the max. It did not move at all until the gauge showed ~10-12 "hg.
I am not sure if this is internal on the actuator or if the turbo vanes are more likely.
I ordered the turbo flange gasket, 3 nuts, and a new stud. I'm going to pull off the downpipe and clean via Easy-Off. During that time, I'll pull the clip off the actuator and independently inspect them both.


What would this mean though? I'm understanding it to mean that very gradual changes in boost command (driving very gently and light throttle) would cause overboost. But driving more aggressively wouldn't?