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)

jcman

Was the CEL on or flashing?
Did you pull any VCDS/Vagcom codes?

If no is the answer to both then a failing fuel pump is a possibility or you could have bad gas "rare".

johnkk

As noted, check for codes. Absent that, it sounds like it might be vacuum leaks or post turbo intake plumbing issues. Look for disconnected hoses, cracks in hoses, etc. I was thinking maybe the MAF, but they usually show symptoms like that only after warm and in closed loop.

acarney

Sadly don't have VAGCOM yet and don't know anyone other then dealer that does. I don't really wanna try to drive my car to the dealer since I need to get on the highway to do that. It does seem to run ok after about five minutes of being on. I was able to floor it once I got to my drive way and it would rev to 5k rpm without stalling and would fall back to a normal idle. Would a vacuum leak big enough to cause stalling on most start also allow it to run ok once it was a little warm? (Remember, only drove about 1 mile and hardly any rpms during that time; can't remember what engine temp showed but I know oil temp hadn't had the time to warm up AT ALL)

I'll check when I get off work today and get home but I'm not totally sure of all the vacuum locations, anyone have any guides or pictures which might help me?

By odd chance the night before I did look under the hood to see if I could see any oil dripping from the rear of driver side engine (valve cover job from last year and I'm getting a slight smell of oil just every now and then) and I noticed the bell shaped thing that connects to part of the intake housing (?) and the spider hose seemed to have some flex in the rubber boot part of it. When I squeezed it it almost came in two parts but it didn't look broken or aged. This was a new Audi part with less then a year on it and the rubber is soft, I just can't remember if the old rubber part had a slit half way up it... Is it to slide the rubber off the actual valve or whatever is inside it? Doubt that's a source of leak but just tossing out what I noticed the night before this issue... The car DID start fine that next morning and took me to work, it was after that and trying to come home that I had the issues

Airbag

id start by changing the fuel filter . Sounds like fuel starvation to me .

acarney

That's totally what I'm wondering. I honestly have no idea WHEN that was last changed... This isn't going to be fun changing with 3/4 of a tank, is it? Also, thinking about replacing the fuel pump too... Anyone know of the quality of the one ECS sells (not the Audi OEM and not the high performance aftermark ones)?

Come to think of it, my MPG the last two tanks has been rather bad (14 to 15 when it used to be 18+ city), honestly can't recall if I've been sitting in the car for awhile with it running and listening to the radio after grabbing something to eat though or what not...

jcman

Ok no CEL light, you did not answer or mention so I guess so.

The ECM will report conditions of many inputs, however fuel delivery is really not one that has ever been diagnosed by codes or measuring blocks but can be verified by a good old pressure test, the list of problem items could be the fuel pump, pressure regulator or a loaded filter as Airbag mentioned.

johnkk

I think this is a good path to follow if no MIL. Vacuum leaks have always kicked on light and threw misfire codes for me. Poor mileage issue and that the car revved up with no load are good fuel clues. I would lean towards fuel pump, only because I've never gotten lucky with just fuel filter in these situations. New filter is in order with a new pump, so I've always been able to rationalize trying the filter first!!

jcman

Maybe someone packed snow in his exhaust and it froze....Naw....I doubt he's a un-popular high school principle or backed into a snow bank.

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?