I am beside myself with this thing. Ever since I installed my headers and exhaust, my runner won't hold an Idle and it keeps surging and dropping about 100 rpm or so and it's eating gas at idle. It idled a little high before until it cooled down. A while ago my coolant temp sensor started acting flaky and dropping from normal to dead and then bouncing back and forth, but it does not happen all the time.

I am wondering if since this engine does not have an idle air control valve, but uses a coolant passage (Idle Air Control Valve Discussion if this could be contributing to my erratic idle.

I also noticed that their is a diaphragm behind the TPS that has a plunger which comes in contact with a screw on my throttle. This has a vacuum line going to it and it is surging. The plunger goes in and out as the idle fluctuatea. even with the vacuum line disconnected the engine surges. Anybody know what this is?

Finally, I am going to give it one last go this weekend and take it in to get serviced if I can't figure it out. If I end up going that route, would I be best to take this to a Toyota dealership or do you think I could get away with going to another service station (BrakeMax or other franchised garage)

your responses are appreciated