Please help!-AHU with bad idle.

Hello everyone, this is my first post here. I've been lurking in the background for over a year reading posts and comments while I worked on my 82 Vanagon swap.
Over a few months ago I swapped an AHU motor from a 98 Jetta into my 82 Vanagon diesel. I custom built the harness, swapped everything over from the Jetta. The fit and finish look great, but the engine just does not idle right. It starts right up every time and it will idle fine for a few minutes when cold. But as it starts to warm up the idle starts to jump around. It will stutter for a few seconds then the engine corrects itself then it stutters again and then corrects itself, it will keep doing this.

I have no faults in the ECU. I have checked compression and all 4 and are at 350 when cold. I made sure my timing was right in the middle with vag-com. I pop-tested the injectors when with an amazon injector tester. They seem to be popping at 250bar as stated on the injector. The patter seems to be ok but I can't say for sure. One thing that I don't like is the injection quantity. It's very unstable, it bounces between 2 and 5 constantly. Also, my MVB13 shows my injector adjustments all over the place.

Here are some videos I took while connected to the VAG-COM. Its a video of MVB 1,13 and 8. I hope this helps to understand the problem I'm having. You can here the engine idle in the background and see the numbers change.

Part 1- https://youtu.be/CHFtDYpuryU

Part 2- https://youtu.be/0p5xYxQ95X8

Part 3- https://youtu.be/ooKXk7-jBPU


Thank you in advance for your help.

Quantity adjustment should be stable at whatever it's set to unless fuel demand changes. I would look closer at the ip. What are the injector measurement at?
You cant just pop test the injectors that simply. There are multiple stages and pulses that are set and that takes specialized equipment your not going to be able to buy off the self.

Mongler98 said:

Quantity adjustment should be stable at whatever it's set to unless fuel demand changes. I would look closer at the ip. What are the injector measurement at?
You cant just pop test the injectors that simply. There are multiple stages and pulses that are set and that takes specialized equipment your not going to be able to buy off the self.

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Actually, he can pop the injectors since at idle they're only using the first stage. They're not rocket science. Lots of us have done it.

Was the pump used or a 'new' one from someone in North Carolina? I have seen this before, although not as bad, and it was a Prothe pump that was to blame. I am NOT suggesting you need a pump at this point.

What did you do with the EGR system? Is it plumbed in and functioning or deleted, and do you have a tune? The EGR system can create imbalances and poor running if not deleted properly or if the system is malfunctioning.

Did you listen to the AHU run before you swapped it? Did it run OK?

The engine was from a junkyard so I've never seen it run before. i bought it in LA so not from NC. The pump is what came with the engine. I originally had the EGR deleted, but decided to put it back on just in case it was the EGR. But putting it back on didn't help. No the engine is not tuned. Not that I know of.

Is your injection pump leaking at all? Any air in the fuel lines to/from the filter?

Do you know how long the engine sat in the junkyard?

I don't know how long it sat at the junkyard. I can't see if there is any air in the lines since I didn't use a clear fuel line. I did install a new tank and new fuel lines. A new filter as well.

Can you post up videos of VCDS logs, 3 at a time, of every one available? It may help narrow things down. I know it’ll take awhile but there are different ones that are of different systems and it’ll help narrow things down.

Can't really hear your issue but my '98 had a bad idle. Kinda rhythmic rmm-rmm-rmm. At slow speed light pedal like in a parking lot it would surge. IQ wandered all over the place as did the injector balance.

Hammered it from one extreme to the other, new balanced injectors, nothing helped. Replacement pump fixed it.

I suspect it was metal particles in the QA hanging it up. Felt smooth if you rotated it by hand but my theory is that when it's powered up the stuff stands up and drags. Haven't gotten around to opening it up yet to see since it requires those welded wire joints to be broken.

Abacus said:

Can you post up videos of VCDS logs, 3 at a time, of every one available? It may help narrow things down. I know it’ll take awhile but there are different ones that are of different systems and it’ll help narrow things down.

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Ill do the logs tomorrow and take a video of it. Any specific value blocks?

KLXD said:

Can't really hear your issue but my '98 had a bad idle. Kinda rhythmic rmm-rmm-rmm. At slow speed light pedal like in a parking lot it would surge. IQ wandered all over the place as did the injector balance.

Hammered it from one extreme to the other, new balanced injectors, nothing helped. Replacement pump fixed it.

I suspect it was metal particles in the QA hanging it up. Felt smooth if you rotated it by hand but my theory is that when it's powered up the stuff stands up and drags. Haven't gotten around to opening it up yet to see since it requires those welded wire joints to be broken.

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I have a feeling its going to be ending up my pump. It goes into rhythmic bad idle then corrects itself. The does it all over again. I wish someone can lend me a pump to try out. I dont want to but a used pump if its not the problem.

This video was taken a few hours ago. My timing starts jumping al over the place as soon as it goes into its spasms. I know the coolant temp was not hot enough but it doesnt make a difference when its above 80C. It still does the same. How can I check my pump to see if its bad? Is there a way to open it up and check for something?

https://youtu.be/4RoLbihQ58Y

Anyone recommend a good rebuilder?

VanagonWestyTDI said:

This video was taken a few hours ago. My timing starts jumping al over the place as soon as it goes into its spasms. I know the coolant temp was not hot enough but it doesnt make a difference when its above 80C. It still does the same. How can I check my pump to see if its bad? Is there a way to open it up and check for something?

https://youtu.be/4RoLbihQ58Y

Anyone recommend a good rebuilder?

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The fact that it does run correctly for a period of time leads me to believe that it can be made to run properly all the time. If it was leaking I'd probably replace all the seals, clean it out, and then reinstall it and get it running again.

I can hear the rythmic pulsation, it doesn't sound like a fuel starvation or air infiltration issue because it's too regular, but I wouldn't rule that out until I had observed a solid fuel feed to the IP.

I'm really curious about what the result of running Diesel Purge through this system might be?

Steve

Steve Addy said:

The fact that it does run correctly for a period of time leads me to believe that it can be made to run properly all the time. If it was leaking I'd probably replace all the seals, clean it out, and then reinstall it and get it running again.
I can hear the rythmic pulsation, it doesn't sound like a fuel starvation or air infiltration issue because it's too regular, but I wouldn't rule that out until I had observed a solid fuel feed to the IP.
I'm really curious about what the result of running Diesel Purge through this system might be?
Steve

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The pump has no leaks. I will replace the feed line with a clear hose to see if I have any air in the system. Does the diesel purge get connected straight to the pump? Or I have to put it in my tank?

You can add it to your tank, run it straight from a bottle or run it from a bottle with the return line going back to the bottle so it recirculates for the most benefit, if any. Should use a filter if running from the bottle.

If using it straight, run it a while to get the stuff throughout the pump then shut if off and let it sit and do its thing.

The Diesel Purge should be run straight. I've never filtered it since it doesn't need it, I just make sure the container into which it's poured is clean. I use glass since it'll get very hot. I have special barbs made up just for the Diesel Purge to connect to the fuel filter hoses.

I agree with Steve, if it were a constant problem it wouldn't have a time it runs normal.

Please provide small videos of VCDS Groups:
003
004
007
010
011
019
021
022

I will make a video of those value blocks and post it tomorrow. I also noticed that my mass air flow reading doesn't match. The actual is higher than the specified when idling. Is that something to go after? When I didn't have the EGR connected the reading was around 500mg. Which was expected since the EGR was deleted. But after I installed the EGR back the readings still didn't match. It went down a bit not exactly what the specified is. I also had changed the EGR duty cycle with bag com. Should I set it back to factory duty cycle?

Definitely post up the video's of the VCDS values, those are going to be the best indications of where the problems will be found. You might try unplugging the MAF while it's pulsating to see if that corrects the issue although I will say that it's rare to see a Pierburg MAF fail.

Make sure that your change to the EGR duty cycle is within the settings recommended for reducing the cycle. I don't believe that this will end up being the cause of your problem.

As for the Diesel Purge I would run it directly, I think the effectiveness is reduced when it's used as a tank additive. Mark's photo is a good method for doing this, just be sure that the line to the IP is always submerged completely in the liquid.

Steve

Guys I think I found the problem. After everyone's suggestions of running diesel purge, I got a bottle of it and put it in a jar. I also got clear fuel lines to see what's happening. I put both the supply and return lines in the jar and started it up. Instantly the engine sounded and felt different. I ran it for good 10 minutes and the the engine ran perfectly. Then I connected the lines back to the fuel filter and return and the engine went back to it's spasm mode. So I'm either getting air in the system or my fuel feed/lines are insufficient. I'll chase this down and see where it leads me. Thank you everyone.

I'm gonna try disconnecting the fuel return and put it in a container to see if my return is causing the problem. Then I'm gonna do the same for the supply to see if the supply is not enough. If my supply is not enough I plan on adding an inline pump to help with the supply. What do you guys think?

Fals alarm . After running the diesel purge I ran regular diesel in the jar and it's still doing the same. It's was just cold. Once it warmed up it started doing the same. I'm gonna send in my injectors to get them checked out.