Took my 2001.4 S4 Avant 6MT for a diagnostic when the CEL came on (of course, within two weeks of buying it). Mechanic ran the codes, said he found a bad EGT sensor code (driver's side - tough swap!), and a misfire in #2 which seemed to be caused by a 'cracked valve on the suction pump pipe."

I couldn't afford the $800 for labor, so I did the job myself with parts ordered from ECS tuning. But when I pinched the gasket on the firewall to remove the suction pump pipe, it hissed and released air, so I stopped - and the noise stopped. Would that not indicate, without a doubt, that there was no leakage from the suction pump pipe, and that I'd received a bad diagnosis?

Please advise - the CEL is back on after being DIY-reset, and I'm not sure whether to remove the belly pan and dig back into the EGT sensor issue or take my concerns to the mechanic.

PS - Who wants to buy a used but probably perfect suction pump pipe?!?