What IAC paramater will slow down the speed of the IAC in the 7427 PCM? It's extend and retract movement are a good bit faster than my original (7060) PCM and that causes a random stumble or surge with my setup. Thanks.

 

The IAC speed itself will be the same. Both have the 0-320 step IACs. The max stepping rate will also be the same (160 Hz IIRC). They should also have similar transfer functions (% airflow vs. IAC steps), but they may differ slightly for a 1 11/16" vs. 2" TBI.

With that said, the actual tune will be different. For a surge/stumble on tip-in Id look at the throttle follower parameters as well as the MAP based acceleration enrichment. Does it surge or stumble completely randomly? Only at idle? During initial acceleration?

 

I zerod the idle overspeed spark retard and it seems to have either eliminated or drastically reduced the stumble it had. Tip in and on the gas is perfect, it was occurring when I was in gear rolling, but not on the throttle (like when stuck in traffic) it would crawl along then act like the spark was momentarily cut.

I'll be sure after I drive it home tomorrow.