you mentioned that you turned the idle down to 1500-ish when the car is warm and it surges...Thats exactly what is supposed to happen. The ecu is stepping the ISC up and down in its search for 750 RPM's.

Try grounding the timing connector and grounding terminal #10 of the diagnostic connector and check your idle. It should be 750. do all this with the engine warmed up.

If it aint close to 750, adjust your throttle cable, biss screw, but dont touch the TPS (its factory set).

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Len...
92 Talon TSi AWD
89 2000 GTX