Merc 8.1S IAC & PCM questions

[Jimmy Buoy]

Mine has a slot for an IAC muffler in the throttle body, but it's never had a muffler. I've never had an issue and might conclude that the muffler if not regularly cleaned/replaced could cause the IAC problem by restricting air flow? I know the same 496/8.1 engine made by Crusader do NOT have mufflers installed. The rubber tube extends from the throttle body right back to the opposite end of the engine which would make any oily "gunk" from the intake area unlikely to actually reach the IAC simply due to the length of travel.

Without the muffler, there is a distinct whistle just off idle - but I can live with that if it means not having IAC issues.

 

[Zephyr]

Finally all sorted!
I had a service tech run a diagnostic scan to make sure there was no other faults and found the only fault detected was an ‘IAC Fault’. Once I knew there were no other issues that could kill my good PCM I swapped the bad PCM for the known good one and the engine ran perfectly.
I got in touch with Whipple Superchargers in Fresno and they were sure it could be repaired. The repair took only a few days and once I received it plugged it in and…..it worked fine.
Jeff at Whipple said it was a bit of a mess in the PCM, when the IAC driver had gone it cooked a few other bits as well.
So for a ¼ of the replacement price I had the PCM repaired and all very quickly – once you take out the 14 days there and 14 days back in shipping and the week customs held it up
Thanks for all the comments and helping me get on track, it’s a good feeling to have confidence in the barge again….I might still steer clear of that anchorage for a few more weeks.
Z.