I have a 1987 Audi 4000CS Quattro with 145000 miles on it. The car currently runs very rough, with the following symptoms:
1) Idle warbles between 800 and 2000 rpm 2) car shudders and lurches, as if it isn't getting enough fuel, when coasting downhill or accelerating uphill. It is roughest when I step on the accelerator or suddenly release the accelerator with the car still in gear.I had the O2 sensor and the idle valve replaced, as well as the cold start valve. The only known issue with the car is a hole in the muffler - my guess is that somehow the hole in the muffler is distorting whatever sensors are in the exhaust system?
I am considering replacing the muffler, but wanted to have a better sense that it is causing this problem.
Thanks for any advice, Audi fans!