ISC motor (fast idle problem revisited)

[MY85pontiac]

i made a post months ago about my carb (holley rebuilt dualjet) and the problem i had about it idling too fast (hot, cold, whenever) around 900-1000 RPM. i believe its the isc motor. the problem im having is this: no matter if the engine is hot or cold it always does this BUT sometimes it will surge (but will only surge in gear). i checked all vacuum lines and they are ok (i even replaced some but it was for the EGR and ported vacuum switch mostly), everything is adjusted properly (i only tweaked the fast idle setting for start up and curb idle, no other screws were turned). it idles smoothly but just fast in park and will sometimes (intermittent problems SUCK!) surge while in gear at a redlight. i am guessing its the ISC motor because i used the one off the old carb and i was having the same problem before i put this rebuilt carb on (i put this carb in for different reasons than this idle problem). also the check engine light comes on ocassionally if it sits running for too long (like in a parking lot) but not if it being driven (like above idle). when the light is on i dont notice anything different and sometimes the light will be on for a minute or so and will go back out. if the engine has been warmed up turned off and turned back on the idle will be at its normal speed of around 750 RPM.

anyone think i'm right about this? i'm tired of turning the car off while in gear because im tired of the engine dieseling because of the excessive idle when i turn it off in park (it hasnt been turned off in park for months now). im thinking if i had this problem before i put this carb on and the only thing i reused was the ISC motor and im still having this particular problem its gotta be the ISC motor but since im not a carb guru i cant be sure.

i have the money for a ISC motor but i just want to see how many people agree with my diagnosis before i actually go buy one.

i seriously need some replies on this guys, help me out please.