1996 350mag mpi Gen+
 

Mefi 1 I was having an idle surge. 500 to 1300 rpm’s. Only code was 42. Cleaned and replaced iac, no change. New ignition control module, cap and rotor, cleaned tb butterflies. No more surging idle. Seems to be running fine. Still has a code 42, after I cleared it by advancing throttle to 100% and back, then pulling paper clip. At this time I don’t have access to a scanner. Anyone have any ideas? Seems to be running perfectly fine. Thanks

If it is running fine I would just run it. One more item to check is the wiring to the knock sensor. That can trip some funky codes. I personally have not had that happen but I think some others have. Your original surging issue I would have guessed to be vacuum related, leaking hose etc.

Thank you, I may just put a new knock sensor on it and ck the wire routing

Knock sensor related codes are 43 and 44.
42 is "Ignition Control Circuit (IC) Grounded or Open Bypass"
Is the 42 code actually clearing though??

Griff
 

On the trailer, cleared the code by that method. Rechecked, no code. Put it in the water, runs great. I check it when I get home, code 42.