A4 Lemon

What basically happens is the motor seems to be failing at fuel enrichment when applying throttle. I have to apply throttle slowly or the car jerks violently. I replaced all the plugs since they had 113k on them...didnt fix it. A month ago one of the coil packs had gone bad but only had money to track down the bad one and replace just that. When the bucking started I got one more coil pack and rotated it from cylinder to cylinder to see if any of them were bad. They werent. I unplugged the MAF and it didn't go into limp mode and improve things at all...was hoping that was it. An hour ago I pulled the plug to the map sensor on the IC and suddenly the jerking stopped 90%. Does this sound like a bad sensor, or does unplugging it force something else to not function...whatever it is that could be bad, like the waste gate or anything else? Im a former engine machinist/builder and built plenty of my own hot rods, but I've never lifted a finger to learn anything about this car...these days it's all about taking care of my family...no more fun ;-)

raj99

I'd recommend you post in the actual subforum specific to your model of A4...B5, B6, B7, B8 and then also append a VCDS log to the description you've provided.

IknowHuhA6

I was going to say kudos for knowing what limp mode is.... then read your hot rod experience and made sense.
I'm relatively new to troubleshooting Audi's as I've primarily built and tuned turbo and supercharged 3800's in the past.
I'm excited to start learning this platform.

I assume you've got a supercharged 3.0 since you mentioned an intercooler and I know the map sensor is mounted there on mine.

So just curious, have you looked for vacuum leaks yet? Do you have any scans of the 02 sensors to see if these are possibly failing and causing a rich or lean condition under load?
But based on what you said, wondering if the map sensor is bad or the signal is getting shorted.

A4 Lemon

Oops! Had a 2 year old trying to get my phone...its a b7, 07 a4 2.0. The IC is buried on the right, and im assuming thats boost pressure sensor of some kind so i assumed its a map sensor. I did use a little scanner and came up with 11 codes... misfires, but that's from when my coil pack failed. The po238 I think it was, from unplugging the map...this thing puts out codes and then goes to words, which is weird. Like it gives codes for misfires and map, but then says o2 heater, but no o2 code, so I'm not sure if I'm reading it right...I borrowed it from my brother. And yeah, I've known what limp mode was 20 years ago from my 87 Buick GN and my Cobra and playing around with that tuning. Anyway, I saw 7 codes one time on this car for totally unrelated things, when all I had was a bad pcv. So, I'm not worried about the 11 codes since alot of them seemed transient from some old issues that came and went awhile back. I don't see a bad 02 causing this when the engine is cold and still in open loop.

A4 Lemon

And btw, what's a vcds log?

transman

Test the map sensor with a multimeter. If you need all the diagnostic info, as far a voltage specs and pinouts, PM me and ill send the info over toy you. I believe I have a voltage to RPM chart on my computer at work.

A4 Lemon

Thanks. I actually figured this out a couple months back. Somehow all 4 of my coils became marginal simultaneously. Replaced them all with 25 dollar autozone coils and it was fixed. I used to know another guy on a mustang forum who went by the handle transman, named Mike. That isn't you, is it?

transman

Naw, I have not been on a mustang forum before. I do use this username on other car & truck forums though. I enjoy answering the diagnostic, and transmission related questions on forums, so I use this username so people can infer that I might be able to help them with transmission issues.

IknowHuhA6

Interesting.... how about the 3.8 SII forums? Any experience participation there?

transman

I dont post on the GM s2 forums, but I do browse a lot. I have been lucky to get to do a lot of cool stuff on them over the years. I build some pretty nasty 4T60e transmissions for them. Imagine having a series two with like 12psi. ARP head studs and stalled with pretty high line pressure.
With the right tires you can get one off the line pretty quick with a stall convertor

I'd have to say a 3.8 series II or a ford 3.8 supercoupe would be one of my favorite american engines.