1996 Ford Escort excessive fast idle & extended

Rpm does not drop until pcm decides to, had several codes, main one P1506, has another pcm, switched MAF, whole throttle assembly, no change. Also, when driving idle races very high, only way seems to fix is unplug IAC valve, but then code will come in. Another noticed affect is when you unplug TPS with motor running it makes idle go high again, eventually it will come down, 1-3 minutes. Also, switched IAc, no throttle binding, no apparent vacum leaks, has had intake gaskets too. Noticed also when you put in drive or reverse the idle speeds up, it seems whatever affects the motor vacum makes it speed up. Also, had whole wiring harness out from IAC & TPS to connectors on fender well, no shorts found. Any ideas, thanks for any help, my first time here nice site.