I have a 2002 3.0 quattro sedan with 148k. I bought this in november from the original owner with all service records. The vehicle has been running great until a month ago. Sometimes the speedometer wouldn't read accurately as well as the fuel gauge, and because the speedo wouldn't read, cruise control wouldn't engage or wouldn't stay engaged. The 2nd issue was an incredibly rough idle, the left muffler smelt funny, and it only happened then the car would be warmed up, never cold. After a few weeks that issue grew, it usually idles around 800 RPM, now it goes from 800 to 1200 and will plunge around 500 and back though the same cycle again, almost stalling. After taking it to auto zone who does free diagnostics, it reads these 2 codes...P0025( camshaft actuator sensor) and P0501(speed sensor). Taking The speed sensor out of this(easy fix), the first code is this as simple as replacing both camshaft sensors??? The alternative reasoning for this code was timing belt jumped teeth; but when I am on the throttle it runs fine again, to me this rules out timing belt as that problem would get worse as RPM increases. Anyone else have this problem????

 

replace the cam sensors. if that fixes it all is good! if not take them back, and let us know

and you say it only does it when it's warmed up? i'd also almost be willing to say CTS sensors. but give the camshaft sensors a whirl.