Ive been having what seems like TPS issues since I swapped the engine in my GST. For the most part the car drives fine. But when I let off the gas say at 2500rpms...the AFR will drop to ~12:1. Before the car would jump to ~17:1 and then read LEAN on decel.

I wouldnt really care but its screwing with my fuel trims real bad. When Im slowing down with the car in gear, since its running at 12:1 it tries to lean itself out. So when I take it out of gear and it starts to idle the AFR is really lean (16-18:1) from the ecu pulling fuel. It will do the same thing when switching gears depending on how fast I shift. Ex: when I shift from 4th to 5th just cruising, it goes 12:1 when I let off the throttle and then right when I get back on it it runs at 15.5ish for a second before it richens back up causing a hesitation.

Another thing to note is that when I decelerate from about 4-4.5k rpms, it will do its thing like normal, and then right around 2200-2000rshared_pm it will jerk and go all the way LEAN like it shutting the injectors off like its supposed to. But as soon as I see the gauge jump lean it starts jerking and then runs rich again.

Ive tested the TPS every way I could find and it seems ok. Resistance is in spec. I pulled the throttlebody and set the TPS with a feeler gauge (.45mm) twice to no effect. When the throttle is closed the idle switch circuit is closed. As soon as I put the feeler gauge in it opens. It takes about a 50mV rise to open the switch. I probed the harness while its powered, and the TPS reads 4.96V when opened all the way.

Is there anything else I can try or should I just bite the bullet and replace the TPS to see if it helps? Also, is there a pin at the ECU I can check to see if the idle switch circuit is in good shape?

THanks!!