01 S4 Avant check engine light with code PO300 Random/Multiple Cylinder Misfire
Reset light and it hasn't come back on, car runs fine. What could have caused the error??

 

Things that can cause misfires, bad/incorrect spark plugs, bad coils, bad injectors, bad ingnition control moduals ande85 gasoline

 

faults listed are spark plugs, plug leads, injector(s), ignition coils, low compression, wiring but since its running ok and no CEL the problem must have cleared its self but a soft error code will have been stored so it need to be cleared

 

try cleaning the maf sensor with a can of crc maf sensor cleaner, I was getting the same code and a rough idle due to a dirty maf. cleaned it, took care of all my problems

 

i have an 02 A6 2.7T Quattro, and can't figure out how to reset the check engine light after replacing my mass air flow controler (big round thing between airbox and intake manifold) any suggestions?

 

VAG-Com, or most any Auto parts store can reset it.