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TPS Sensor Adjustment
Category: Engine Control
If your idle is funny, on a Ford, you've just found the solution!
Throttle Position Sensor:
The TPS is a potentiometer (fancy electronic term for a variable resistor) wound in a semi-circle so that it can follow the action of the throttle.
The throttle controls a "wiper" that travels along the length of the resistor picking off the voltage corresponding to it's position on the resistor. Since you have 5 volts at one end and ground at the other, then the resistor is "dropping" 5 volts. You get your choice of voltage from the wiper terminal by moving it back and forth. Which the throttle action is attached to.
See?
BTW, it's output is the dark green wire with a light green stripe. The other two wires will never change their voltages. They are VRef (+5v) and ground.
The TPS should output EXACTLY .98 volts at idle, on a 5.0. On a 2.3 it works better at .90 volts at idle.
If after checking it as below, you can't get it to xx volts, then drill the holes bigger to get it there.
To adjust the TPS, unplug the IAC motor, start the car, set the idle to 750 +/- 50 RPM for a 2.3 engine, or whatever is specified on your underhood emmissions label, with the throttle stop setscrew. The setscrew is like a carb idle speed screw. It sets the throttle opening baseline on the linkage. Then turn off the car, plug the IAC back in, and set the TPS voltage to the spec. Slowly open and the close throttle, checking the voltage. If there are any glitches in the voltage anywhere in the throttle movement, replace the TPS. This is easier to see with an analog voltmeter (one with a needle, not digital) TPSs go bad all the time.
If your idle is still wandering around, then clean the IAC. (see other tip)