tootrn

I had installed a '96 TT motor into a '96 C4S, it included a '96 TT ECU and harness from engine compartment to ECU. On start up it idles fine but when I go off idle, it doesn't matter how high the RPM, the CEL immediately comes on, even though the engine is sounding strong, and when I drop it back down to idle I get an occasional misfire. Using the Durametric tool I got a code 75 which is a nonspecific misfire. After clearing the fault code and restarting it, it goes through that same cycle: idles fine, no CEL, go off idle CEL comes on, return to idle get misfire. I had double checked all vacuum connections I see no issues there. I'm totally stumped any feedback will be much appreciated.

Quadcammer

code 75? You mean P0075? If not, thats not an OBD II code I recognize.

Realistically, on an engine swap like this, I think you really need to recheck all the wiring.

have you tried swapping a DME from a different car?

tootrn

Code 75 corresponds to code P0300 the text is "Misfire damaging to TWC(Three way catalytic)." Supposedly the engine , DME and wiring harness came out of the same car. I will recheck the wiring and if that's not it will swap out the DME. Thanks for your reply.