So I'm working on a 2003 Audi a4 avant 1.8t, and it is throwing multiple codes. I am a mechanic but, not and audi mechanic. i have owned 3 1990 audi 90s but when it comes to the new ones im lost.
the codes are:
confirmed
p0501 Vehicle speed sensor A range/ performance
p0507 idle air control system revolutions mer munute higher than expected
p0300 multiple misfire
p0301 cylinder 1 mis
p0130 O2 sensor circuit bank 1 sensor 1
p0299 turbocharger / supercharger A underboost condition
p0304 cylinder 4 mis
Pending
p0322 icgition distributor engind speed input circuit no signal

now when i first scanned it i didnt get the p0322, p0300 and p0304. i started with changing coils and plugs to see if that would fix the mis. then i cleared the codes and it was good for the day, then the next day it was worse. I had more codes (all the ones above) and it started dying on me randomly while driving around town.

i have done some research and i get mixed answers. is it an exhaust leak, vacuum leak, pcv, i dont know. I dont want to start throwing parts at it and wasting money to not fix the issue(s) i feel like it is not as many issues and the computer thinks it is. If anyone has some ideas please help.

 

The first thing I'd check is the ground straps that ground the engine to the body of the car. Also loosen and re-tighten any grounds you find in on the engine wiring harness. This will reseat them and re-establish a good connection.

The best way to check the PVC system is to fire the car up and at idle loosen the oil filler cap. Pull gently on the cap as if you're going to remove it. If you feel it being sucked back into the opening, the PCV valve has probably ruptured the diaphragm in it. But you're not getting any "lean" error codes so it's probably not that.

But check those ground straps. Make one if you need to.. There should be at least one or two ground straps connecting the engine block to the body of the car. The mounts will actually insulate the engine so ground straps are necessary.

Be sure to clear the codes each time you make a change.

 

Actually quite the opposite happens with the oil cap, it more like it blowing it off with the rythm of the exhaust almost like the exhaust is exiting through the crank case. I know that's not the case though that just the best way I know to describe it. As for the ground wires I will check those in the morning. I actually haven't worked on it in about a month and it had a very hard time starting today. I had to hold it wide open to get it to start. It's beginning to make me think it's the head gasket but I have no smoke or evidence in the oil or coolant.

 

I don't have a lot of experience with the turbo engines but here's what I think is happening. There is a check valve of sorts that prevents boost pressure from the turbo from entering the crankcase via the PCV system. It sounds as if that has failed and is dumping pressurized air into the crankcase. This will also prevent the boost pressure from rising to the point to where the sensor is happy (tripping the P0299 error). I think it's called a diverter valve. It should be located between the turbo and the PCV. I think once you get the boost leak under control, the other codes will also.