Most vehicle systems use the standard 5.0 volts on the supply line. Try settings your adjusted voltage to .5 volts, and tighten it down. Do this with the throttle in the specified position (usually against the throttle stop) and rotate it until you reach the .5 volts, and tighten it down. I'm sure you already know how to test to make sure you have ground, the correct reference voltage, and that you have the correct voltage change through the range on the signal voltage. The idle condition may not be within the TPS. Look for any vacuum leaks, sticking injector, or voltage drop to the TPS. Some Throttle Position Sensors cannot be adjusted with a meter, and yours being heavily modded I wouldn't swear your TPS voltage will be typical. I have found many times the EGR to be the culprit for an idle problem. If you can't find it within the parameters of your computer, then you must start looking at a mechanical reason such as a sticking EGR, a vacuum leak, a leaking intake gasket. You may have to crunch the numbers on the O2 readings to make sure its not out of range from normal. A problem such as this can drive one to drinking. One other thing I can think of is; one of the plug wires being too close to any wires that go to the computer, and needs shielded.
Glad to help you, Good Luck!!!
Certified Master Mechanic, Shop Owner, 40 years experience.
· 1 decade ago