You're doing way too much guessing. The throttle position sensor has very little to do with engine performance and nothing to do with fast idle. A problem with this sensor will set a diagnostic fault code, and you can test them real easily with an inexpensive digital voltmeter.
What did you do to "reset" the Engine Computer? If you disconnected the battery, that isn't going to fix anything but it did erase any diagnostic fault codes that might have been stored in it. Now that valuable information is lost. Many codes that could lead you to the circuit with the problem won't set unless a number of conditions are met, and that often means they won't set while just running in "park".
Since we know there's no fault codes now, it won't hurt to confuse the issue. With the engine running, unplug the idle speed motor, THEN stop the engine. The Engine Computer is supposed to retract the pintle valve when you stop the engine in preparation for the next cold start. We want to see where that valve is before you turn the ignition switch off. With the motor unplugged and the engine stopped, remove that motor, then look at how far that valve is sticking out. I know you don't know how to gauge that yet but you may get an idea shortly. Try to pull that valve out of the motor body some more. It is going to pull really hard but it can be done by hand. If you can move it more, but not more than about 1/8", the computer already had it commanded out to block air flow in an unsuccessful attempt at lowering idle speed.
Now try pushing the valve to the fully-retracted position. This can also be done by hand but it's not particularly easy. As I recall, the full travel of that valve is about 1/2". If you absolutely can't move the valve at all, the unit is locked up. I've never run into that yet. Failure of these idle speed motors is not common. If you can move the valve by hand, pull it all the way out, then reinstall it that way. Do not plug it in because we want it to stay right where it is. Start the engine, then observe the idle speed. If it is real low or you have to hold the accelerator pedal down 1/4" to get the engine to start, that valve has not been moving and we have to figure out why. If idle speed is still too high, there's a vacuum leak. Having a vacuum leak is when you find the idle speed motor already fully-extended from the computer trying to reduce idle speed.
What is your symptom of overheating? The engine can't get that hot in a minute or two, but a leaking cylinder head gasket can dump combustion gases into the cooling system where it will pool under the thermostat and prevent it from opening. Thermostats must be hit with hot liquid to open. Hot air won't do it. There's a chemical test that can indicate if a head gasket is leaking.
Does the upper radiator hose get real hot? If it does, you may just have a high idle and a fan problem. If the hose stays cool, no coolant is flowing. Don't overlook the need to burp the air pocket out from under the thermostat. There's a bleeder screw on some thermostat housings. On other engines there will be a threaded plug or a sensor nearby that can be unscrewed.
There can also be a vacuum leak under the intake manifold. If a leak is suspected, your best bet is to locate a smoke machine from an auto parts store that rents or borrows tools. That will allow you to inject a white, non-toxic smoke at 2 psi into the intake system, then you look for where it's sneaking out.
Sunday, October 26th, 2014 AT 11:48 PM