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Discussion Starter · #1 ·
The thrill of victory...the agony of defeat. [still not fixed, see below]

Here's the thing: I'm the original owner of a chipped 99 manual 1.8T with 105K miles. It's been idling erratically for the past couple weeks. Not all of the time. Sometimes runs like a champ, other times barely at all. First noticed it coming up to a stop or tooling through a parking lot...push in the clutch...and the rpm's would bounce from 1000 to 500. It would stall most of the time. Then things got worse. Sometimes I'd be on the turnpike motoring at 80+ and it would just turn off. No joke, car would shut off. After a couple of times I realized that if I just turned the key back to off, then on [without cranking the starter] the beast would come back to life. WTF?

I've spent every waking minute for the past week searching the archive for help. This weekend I replaced my stock battery. No change. Then I pulled the throttle body and cleaned it. Big change! The idle is almost back to normal. Took it out for a test drive and thought all was well...then it just turned off. On a flat, straight road...going at a steady pace [maybe 35-40mph]...boom just turned off. WTF.

Someone please tell me what's wrong with my car.
 

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I've the same problem, also a '99 BTW. It is less serious than you describe, but my car also stalls.

I really put my foot in my mouth last week when I reported that I solved this problem through better grounding. It has since resurfaced and I can report only that I have improved the idle and 'cornered' the problem into being an issue that manifests only when the AC compressor is compressing with my better grounding in effect.

Before fooling with the grounding, the idle could dip at any time, especially when maneuvering around parking lots just like you say, but the car would verge on stalling out only if I had the AC switch pushed in (whether or not the compressor was compressing). Now the idle is rock solid in all situations, even with the AC selected, but it still freaks out when the AC compressor is compressing.

If you haven't scanned for codes I suspect you will find none.

The next things I plan to do include 1) trying to ground the AC, 2) replacing the air intake temp sensor 3) and ripping out and replacing all the vacuum lines and check valves. Whatever the case, I have a strong suspicion that this is an electrical or logic problem with the ECU rather than an air intake issue. If the MAF (which I cleaned) were bad enough to cause this I would think I'd be likely to see a DTC about it. I have excellent fuel economy, so I don't think the MAF is the issue.
 

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Discussion Starter · #7 ·
but the car would verge on stalling out only if I had the AC switch pushed in (whether or not the compressor was compressing). Now the idle is rock solid in all situations, even with the AC selected, but it still freaks out when the AC compressor is compressing.
I noticed a correlation with the AC just this morning on my way to work. I was sitting at a light, the compressor kicked on, and my tach dropped to a steady 650-700 rpms. It sat there and stuttered for maybe 5 seconds before I gave it some gas and it returned to normal.

When the car has shut itself down on the highway, I've never noticed if the compressor was coming on [too busy trying not to kill innocent people]. It's weird when it happens though... no warning, or hesitation. Just shuts off.
 

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I may be mistaken, but I believe that the computer maintains a history of CEL’s until cleared (battery disconnect or computer clear). So, you might try locating someone in your area with a VAG-COM. They could read the codes for you. There is a VAG-Com locator file in the info forum.

With your mileage, I would suspect some possible combination of the following:

1. Dirty throttle body: especially with your mileage. I believe that this may be your source of idle fluctuation; especially if you have not performed this cleaning.

2. Dirty/or going bad MAF. Try cleaning first. This will save you $$, vice the replacement. There is a simple procedure to clean this part. Takes about 30 minutes tops. Perform a search through this site.


3. ICM going bad. There is a simple procedure to check this part. Perform search through this site.

4. Vacuum leak. Get a flashlight and a mirror and start looking.

Good luck
 

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Discussion Starter · #11 ·
Thanks for the help. I cleaned the TB last weekend. It seemed to have stabilized the idle, but the car still isn't right. Turned off 4-5 times this morning on the turnpike [doing 75, 3100 rpms, no AC, barely on the gas].

Tonight is the start of my "major overhaul weekend extravaganza":
timing belt,
water pump,
plugs,
vac lines,
air filter,
fuel filter and,
oil and dipstick holder.

I'll follow your suggestions and throw in the MAF and ICM for good measure. I figure if I just throw everything I've got at it...something is sure to stick :lol:
 

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I doubt if the first seven items you list will have an effect (though of course all are excellent things to be doing at this mileage) but as to the last two, MAF and ICM, in the interest of science here at the Club you might test the car after each item to help determine the actual culprit for your symptoms. Inquiring minds want to know. God I love this site. For situations such as this, no one can touch CluBB5.
Good luck this weekend and keep us informed.
 

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What follows is a guess...

I think you may have a couple different problems. The rough idle and the drop in RPM when the AC kicks are likely caused by the same thing (I can't add to the suggestions above, though I really doubt it is the ICM), but the car suddenly quitting while at speed is a separate problem.

My first guess is you have a faulty ignition switch. It goes open intermittently and shuts off the engine. Try wiggling the key around to see if you can reproduce the problem. If that isn't the cause then I'd look for some other electrical fault to the ECU or the ECU itself. I remember one thread by Scotaku where he spent a long time tracking a similar problem. It may not be the same thing, but it is worth reading for the information; he tried a lot of things before he fixed it.

Here it is...

http://www.clubb5.com/forums/viewtopic.php?t=60604&highlight=

Good luck.
 

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Discussion Starter · #15 ·
I doubt if the first seven items you list will have an effect (though of course all are excellent things to be doing at this mileage)
These things have been on my to-do list for quite some time. I didn't actually think any of them are the culprit either. Although, a simple vacuum leak would be a blessing.

My first guess is you have a faulty ignition switch. It goes open intermittently and shuts off the engine. Try wiggling the key around to see if you can reproduce the problem.
I thought this too. I wiggled, twisted and shook it out of frustration one day. Had no effect.

Thank you all for your insight. I'll keep plugging away at it and keep you posted.
 

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I know it's alot of work, but checking after each improvement to see what the problem may be is really the only way you can help save another Passat.

I could be way off base, but my thought is the fuel filter. When was the last time it was changed? Could it be clogged enough to let alittle gas through, but not enough to compensate for the drop when you take your foot off the gas? I see it's on your list to change when you do the TB.

The only other thought are the vacuum hoses or a vacuum leak.

GL
 

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Discussion Starter · #17 ·
The victory: Using DaddyMatt's sweet write-up, I was able to replace my timing belt this weekend. What a sense of accomplishment.

The defeat: Since the car was in pieces I decided to do a bunch of regular maintenance things. I thought for sure that replacing the fuel filter or vacuum lines was going to solve my stalling problem. Long story short... no dice.

Jaero: Thanks for the tip on Scotaku's ECU issues. I read the posts and they seem to be a dead on description of my problems. I called AWE this morning and made an appointment for them to check out my chip next week. I'll keep everyone posted.
 
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