98 DOHC Taurus idle issues w/codes
My recently acquired 98 wagon has had a few issues since I got it. The IAC was unplugged so I hooked it back up, cleared codes and drove a bit to get ready for smog. On the test drive it feels almost like the cruise is on (ie letting off of the gas pedal doesn't allow for much coasting or slowing down). If I shift into neutral while at highway speed rpms will hit around 3000-3500 with the throttle closed. If I allow this to continue for a a bit I get a code P1120 which means TPS input is lower than MAF. I still get decent idle control in gear stopped, at low speed and in neutral parked. I have checked the TPS signal at the ecm pin with my voltmeter and it is within range, however the scantool readout shows the TPS voltage to be responding to change a lot slower than all the other sensors. Eventually the scantool reads actual tps voltage, it just takes a while (ie 5 seconds from closed to wot, 5 more seconds back to closed) to get there. PCV and all vacuum systems appear working and not leaking.
I'm thinking the IAC is either worn/malfunctioning or maybe the ecm is faulty and sending the wrong signal. My scantool doesn't really let me monitor the IAC commands. Any ideas or suggestions would be much appreciated. Thx.