2002 A6 2.7t almost didn't get me home; stalling as soon as I hit the gas? Help?

[acarney]

So I have a 2002 A6 2.7t (auto) with ~170k miles on it. I replaced battery and alternator last winter (almost exactly a year ago) when I was doing a timing belt/water pump/valve cover gasket job. Battery has been strong and never slow to start or left me stuck even on the coldest nights this year. So I don't think it's that... now... the issue.

The car has been starting fine and running fine but today when I left work (about 7 hours after getting there, car hadn't been started at all during that time) it had a big issue starting. The key would turn and the engine seemed to turn over fine and strong, but wouldn't start. If it DID start it was for like half a second to one second when the rpms would jump to about 1,000 and then almost immediately stall. I did this about six times with it starting maybe four out of the six but stalling right away. Each time it seemed to start strong but just wouldn't catch and when it DID for that second or so before stalling it sounded HORRIBLE and really weak. I let it sit for a few minutes trying to think what it might be. Started it again and pounded the gas AS SOON as it started, expecting at least a quick roar before maybe stalling, instead it was like a kill switch, it died the SECOND I floored the gas. Did that a couple times with no change. Decided to hold the gas pedal to the floor and try to start it while doing that and it wouldn't catch and start at all, again, started and battery power seemed strong. Decided to try the opposite of that and be SUPER gentle on the gas as soon as the engine caught and I was able to push the rpms up to like 1200 for maybe three or four seconds while it sounded rough and really uneven (misfires maybe? Just really weak, like hardly running but it was showing 1200 then bouncing down to maybe 200 and then back to 1000 and back down again and then stall). I did this a couple more times while being SUPER gentle on the gas and it got better each time till finally the 3rd or 4th time it didn't stall, but still sounded weak and really rough. I let it run for maybe a minute just keeping a super steady gentle pressure on the gas till the engine sounded almost normal. Then I pushed down harder and it ALMOST stalled so I let the gas up right away and it coughed a couple times and leveled out at ~600 rpm again. I was able to rev it up to maybe 3000 or 4000 rpm if SLOWLY using the smallest increasing amount of pressure on the gas. After about two minutes of the car running almost normal sounding between 1,000 and 3,000 rpm I decided to put it in gear and see if it would stall (didn't), then letting off the brake and seeing if it would roll without stalling (it did roll), and then decided to drive home the back roads going super gentle since I only had about 1 mile to go on residential streets that are almost always empty. It made it home but seemed to cough a little bit once when I pushed the gas a little harder off a stop sign. If i was super gentle I could get it up to like 10 mph fine (didn't try going above that) and transmission seemed to shift fine on it's own. Battery was showing ~14v. By the time I made it home and into the driveway I floored it while in park a couple times and it sounded basically normal again. Strong sound, normal amount of lag, full rev without shutter. Turned the car off, talked to family about my day and had dinner. Went out just now after 3 hours of it sitting there and it did start on the first try while my foot was off the gas but seemed to be shuttering and when I pounded the gas it would dive down to like 200 revs and almost stall before starting to rev up again to maybe 2500 rpms which was when I let off the gas again. It would shutter a little and then level out at normal idle. Pound the gas again and it repeated the same thing. Decided to turn it off and come report back to you guys. I'm catching a ride to work tomorrow just in case she doesn't start in the morning or make it home from work, easier to work on it here then in work's parking lot, lol

What do you think is the issue? Recommended parts to replace? Links to DIY/parts? Thanks guys!!!

(Sorry for the long post, just wanted to provide EVERY bit of details and info I have... also, yes it had gas, about 3/4 a tank)

[LINDW4LL]

Try unplugging the MAF (mass air flow sensor) and see if it runs normally. It's located after the accordian hose, before the airbox. If that fixes it, MAF is bad. Common problem.

It's really hard to know without codes though. Stop at Autozone and have them scan the car if the MAF trick doesn't work.

[Wagonholic]

Could also be a REALLY BIG boost leak.

[acarney]

Could also be a REALLY BIG boost leak.

Would that be likely without any issue before? Car has been starting/running awesome up till this afternoon leaving work, in fact this morning GOING to work it started right up and seemed fine. Hasn't seemed down on power either and no weird sounds/hissing or anything...

[Wagonholic]

Would that be likely without any issue before? Car has been starting/running awesome up till this afternoon leaving work, in fact this morning GOING to work it started right up and seemed fine. Hasn't seemed down on power either and no weird sounds/hissing or anything...

Yes, a hose could have popped off. Happened to me. Ideally you'd want to do an intake pressure test at 15psi. Super easy to do, and any leaks in the system will be exposed. Any intake/boost leak can make the car run like crap since it skews up any air readings the MAF gives. Even a tiny leak. The same exact thing happened to me. When you unplug your MAF the ECU basically guesses how much air is coming into the system. Which is why you can actually drive the car with the tbb completely off if the MAF is unplugged. That happened when my tbb fell off. It is also why you don't have ESP/ABS with the MAF sensor unplugged, as the whole system is based upon air intake readings.

Do a boost leak test, if there are no leaks it's probably your MAF. If there are leaks, fix them and see if the car runs fine. Make sure it is a pressurized test, as some leaks are only noticed when the system is under pressure. Google AWE's instructions. I got the materials I needed for around $10, not including the air compressor lol. A standard non-pressurized smoke test may not reveal all leaks. It must be a pressurized test.


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[Wagonholic]

When you have a leak post-MAF air that has been accounted for is escaping. So the engine is getting less air than it is expecting which can result in the car running rich and/or basically drowning itself in its own fuel.


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[suth31]

When you have a leak post-MAF air that has been accounted for is escaping. So the engine is getting less air than it is expecting which can result in the car running rich and/or basically drowning itself in its own fuel.


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^ Yes this happened to me when I had a boost leak. Do you get any rotten egg type smell? I had the smell when my throttle body boot came off, and my car bucked and hiccupped and I thought for sure I broke something. Luckily the tbb was right up front and easy to see/fix, and was loose as a result of me messing around a week or two earlier. I also experienced another boost issue where I had under-tightened a turbo-to-intercooler hose, and that blew off while driving - that killed my car on the spot until I looked underneath and fixed up the hose. Again this was due to my replacing the hose and not tightening it enough. Its possible that you might be experiencing a similar issue since you stated that you recently preformed a timing belt service. And yes, also check the MAF as those do go bad. Try unplugging it like others suggested, just be aware that you will get the ABS light on in your dash until you reconnect the MAF. Good luck and report back

[Brandon002]

Definitely sounds like a MAF issue. Typically with a bad MAF you'll get that stall when you try to take off from a stop.

As other's said, try unplugging the MAF, then starting the car. If the problem gets better, your MAF is faulty.

Do you have a VAG COM or other appropriate AUDI scan tool?

[acarney]

Definitely sounds like a MAF issue. Typically with a bad MAF you'll get that stall when you try to take off from a stop.

As other's said, try unplugging the MAF, then starting the car. If the problem gets better, your MAF is faulty.

Do you have a VAG COM or other appropriate AUDI scan tool?

I don't, not yet at least. Do you happen to know if that cheaper second link (Amazon) one can reset and clear CEL and codes on Audi? Or does it just decode the VAG codes more to plain text?

[acarney]

Tested it when I got home, car stalled right away. Unplugged the MAF sensor and it still stalled. Kept trying and it would do the same hung, turn over strong, catch, just to about 400rpm for half a second and stall.

Kept doing this a couple times while punching the gas as SOON as it fired up and I sware it stalled faster. Kept my foot to the floor on the gas WHILE I started it and it wouldn't even run for that half second, it sounded worse. Finally after about ten times trying to start it I got it to catch and SUPER carefully gave it a little gas so it wouldn't stall. Very gently worked my way up to like 4,000 rpms and then let off the gas and it fell down to a normal idle. At this point it acted normal. Floor it and it would roar up to 5k rpm, fall back to normal idle, etc.
Shut the car off and restarted it like four times each time with no problem at all. Strong fast start, high revs fine.
Left the car for about half an hour and tested it again, started and revs fine. I'm curious at what point it gives me the stalling issue... I figure it's around the 2+ hour mark... I'll test later before bed tonight.

With this new info, can we rule out anything? It still sounds smooth as heck when I finally did get it running and steady idle (ironically I sware it's more steady the usual :P). Would a vacuum leak bad enough to cause the horrible stalling issue (taking like fives minutes and like 15 starts) but leave it running great once it is started?

[Wagonholic]

Tested it when I got home, car stalled right away. Unplugged the MAF sensor and it still stalled. Kept trying and it would do the same hung, turn over strong, catch, just to about 400rpm for half a second and stall.

Kept doing this a couple times while punching the gas as SOON as it fired up and I sware it stalled faster. Kept my foot to the floor on the gas WHILE I started it and it wouldn't even run for that half second, it sounded worse. Finally after about ten times trying to start it I got it to catch and SUPER carefully gave it a little gas so it wouldn't stall. Very gently worked my way up to like 4,000 rpms and then let off the gas and it fell down to a normal idle. At this point it acted normal. Floor it and it would roar up to 5k rpm, fall back to normal idle, etc.
Shut the car off and restarted it like four times each time with no problem at all. Strong fast start, high revs fine.
Left the car for about half an hour and tested it again, started and revs fine. I'm curious at what point it gives me the stalling issue... I figure it's around the 2+ hour mark... I'll test later before bed tonight.

With this new info, can we rule out anything? It still sounds smooth as heck when I finally did get it running and steady idle (ironically I sware it's more steady the usual :P). Would a vacuum leak bad enough to cause the horrible stalling issue (taking like fives minutes and like 15 starts) but leave it running great once it is started?

Yes, that sounds like a boost leak. A simple pressure test will reveal any leaks within the system. A boost leak can result in premature turbo failure and/or engine wear.


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[Wagonholic]

^ Yes this happened to me when I had a boost leak. Do you get any rotten egg type smell? I had the smell when my throttle body boot came off, and my car bucked and hiccupped and I thought for sure I broke something. Luckily the tbb was right up front and easy to see/fix, and was loose as a result of me messing around a week or two earlier. I also experienced another boost issue where I had under-tightened a turbo-to-intercooler hose, and that blew off while driving - that killed my car on the spot until I looked underneath and fixed up the hose. Again this was due to my replacing the hose and not tightening it enough. Its possible that you might be experiencing a similar issue since you stated that you recently preformed a timing belt service. And yes, also check the MAF as those do go bad. Try unplugging it like others suggested, just be aware that you will get the ABS light on in your dash until you reconnect the MAF. Good luck and report back

Yep, I had that same smell as well. I have no idea what causes it; probably all the unburnt fuel. It could also be all the carbon buildup/unburnt fuel in your cats as a result of running rich. You might want to check your engine timing fuses (29 and 32) as those can sometimes blow. If they're blown they can through the entire engine operation off.


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[Brandon002]

I don't, not yet at least. Do you happen to know if that cheaper second link (Amazon) one can reset and clear CEL and codes on Audi? Or does it just decode the VAG codes more to plain text?

Which amazon link? I got my VAG scan tool off Amazon for around 70 bucks. It works great for coding, scanning, clearing CEL's and tons of other stuff. Not sure if it's the same one you're referring to though.

[acarney]

It was linked... But when I checked it later it wasn't. Realized I think the message board is auto linking for ads... Which in this case was actually relevant, lol. I'm debating buying the RossTech one since it looks like they have an iOS/universal browser version now... I'm a Mac guy only so it would have been buy a cheap $200 winXp laptop AND VAGCOM just to get it working, but kicks the price up to like $400... Which has just seemed to much for me when I know I'll only use it like once a year, lol.

Anyway, ordered and should have by Friday a new fuel pump, relay, and filter, and a new coolant/engine temp sensor (the one behind the engine on the pass side). I'm pretty sure I replaced that when I did my timing belt job last year, but maybe I got a crappy one. Anyway it seems like others have had the same issue I'm talking about and it's been that... I'll do this, if these don't fix it, I guess it's vacuum line replacement time... The cost isn't too bad on that, it's just a little daunting to me. (Somehow you would think full valve cover and timing belt job would be more scary) I've found a few diagrams and have the repair book, but still it's hard for me to identify all the lines on the engine and I don't want to poke around trying to guess which is leaking. If I'm doing the vac lines I'm doing all them, it's an old car and I don't need one to break a month after I repair another one. Guess I'm trying to avoid what looks like a confusing job... No one happens to have a YouTube video showing someone replacing them on our engine or at least going around the engine pointing each out and it's routing, do they? That would go really far toward me tackling the vac line job...

(Also, Audi quoted me like $1000 for the vac lines... Aren't the kits like ~$100? That must mean it's a lot of labor, which adds to my worry :P)