Idle Loping and Surging

I have a 92 Toyota Pickup 4WD. When I start it up it idles high, like it should, around 1800 RPM. After I drive it for about a minute the idle increases gradually until it is around 2300. The engine is still cold at this point. After around 5 minutes when the water temp gauge is beginning to move, but is not quite at operating temp, I get a surging idle. It revs up to 2300 or so then drops down to 1600 or so repeatedly about once every second and a half. When I step on the brake it continues the behavior but at lower RPMs.(from about 1300 RPM - 750 RPM) About 3 minutes after this, the engine will be at operating temp, and the idle will settle around 750 RPM. I recently replaced the thermostat and drained and refilled the radiator. I have also adjusted the idle because it was generally too high. This has been very frustrating and embarrassing. TIA


Check the idle sensor. I believe that the throttle position sensor on that model was a 1 wire switch with no purpose other than to tell the ECU to take over the idle speed. If there is only one wire ground it and see if the idle smooths out. As for adjusting the idle, did you adjust the throttle screw or the recessed screw with the paint tell=tale on it.

I adjusted the screw on the side of the throttle body. I think it is called auxiliary air control or something like that. It’s recessed in a plastic housing just to the left and forward of where the throttle plate would be. What does the TPS look like?

Oh I adjusted the Idle Speed Control Screw, not the Auxiliary Air Valve

Found the TPS. It has 4 wires coming out of it.

help still happening