High Idle Problems

I have a 94 Sierra with a 4.3L which blew a head gasket about a month ago. After replacing the head gasket the idle is from 1400 to 2100rpm and the trans will not shift unless I lift off the gas. I searched for vacuum leaks, I even ran the garden hose over the engine to listen for changes. I believe there are none. I have replaced the IAC and MAP sensor. The IAC doesnt seem to be closing to anywhere near the seat. I would appreciate if anyone could tell me where the ECM gets the info to control the IAC. I replaced the intake, egr and throttle body gaskets and still no change. There are no codes either. Please any help would be greatly appreciated.
Thanks in advance.