I too am having problems with surging idle, upon searching post in the forum, I have read about setting the TPS to a certain voltage at idle. My question is how is this done? I have a '90 F150/302 with a new crate engine. I have replaced MAP, TPS, and IAC. I have cleaned the t-body and intake with Sea-Foam cleaner with little or no changes. I also notice the idle speed increases when the A/C or defrost is turned on allthough the compressor has been disconnected electrically. Any help on this matter is apreciated.

 

The EEC computer monitors if the A/C clutch is on, or not. However, it assumes that the clutch closes, and whether it does or not is actually irrelevent. It will increase RPMs anyway by about 100 RPM or so.

To adjust the TPS:
1) Loosen the two screws holding on the TPS, (The screws can be very stubborn, so make sure you have a good quality screw driver that fits snug and has a long handle for lots of torque, or you might strip the heads) just enough to able to swivel the TPS with force.
2) Pierce the "GREEN" wire with the pin and hook the positive (+) lead from the voltmeter to it.
3) Ground the negative (-) lead from the voltmeter. Use a good ground, like the engine or other grounded metal source.
4) Turn your ignition key to the run position, but do not start the vehicle
5) Rotate the TPS until you achieve .98 to .99 Volts (For stock or slightly modified engines).
6) Tighten the screws on the TPS and recheck.

 

My '90 302 does not provide any adjustment of the TPS, the mounting holes are the same size as the screws. I use a ohm meter to test the TPS, unplug the wiring and watch the meter as you slowly open and close the throttle. The meter should slowly move without jumping around. Closed throttle = 3 to 4,000 ohms; wide open throttle = 350 ohms. You may have some luck if you take the sensor off and force some spray type electrical cleaner into it and work it back and forth (it helped mine). ...Terry