N-Gon

Bought a used 2009 A4 2.0 Quattro three weeks ago. I haven't been able to take possession of the car yet because there was a CEL. The car ran fine on my test drive. The sales guy said it was a sensor and they they'd change it out. I talked to the service dept. a few days later and they said it was still throwing misfire codes even after checking cylinders for pitting, replacing all spark plugs and coil packs. It's been to the Audi dealership service dept. twice now. The place I bought the car is about 50 miles from the Audi dealership. The car runs fine for a few hours and then throws a CEL misfiring cylinders again. It now has to go back to Audi for a third time. Any ideas what is going on here?

Thanks for any thoughts or other input!

tenspeed

IIRC you're probably seeing a P0300 code - random misfire. Since the ignition side was inspected and/or replaced, that leaves a fuel delivery problem.

Suggest that the shop shop check the fuel pressure at the rail. Perhaps changing the fuel filter and running some injector cleaner through the system. It could also be a flakey air flow or temperature sensor send a false signal to the ECU.

N-Gon

Thanks for the feedback!

If this next round at Audi doesn't fix it, I'll have to bring these suggestions up to them. No idea why they would have had the car twice and not examined the problem further than they have? I guess I'll have to wait until sometime next week to find out.