Idles@2500 rpm until engine warms up - 1989 Geo Tracker

Clean out the throttle body carefully and replace the auxilliary air idle valve. There is a resetting process for this valve so dont just fit and hope!
Check on Google or forums but i think ...when fitted you turn on ignition but dont start car , then put the accelerator pedal slowly to fully open, hold it for a min then release. start and drive car until warm and the recheck.
If the idle is high then settles it is not an air leak. It is something stuck that then releases which is only throttle flap or idle valve. It is always a goid idea to replace fuel, oil, air filters on normal service intervals.
Roger

Starter or alternative sounds like

which car is it?

problem with 1993 Geo Prizm '99 silverado 5.3 engin will not idle runs at 2500 rpm and drops down to 1000 rpm the back up to 2500 rpm -------------------------

TUNE-UP, SPARK PLUGS, WIRES, AIR & FUEL FILTERS, FUEL INJECTOR CLEANER IN TANK, ALSO REPLACE PCV VALVE, & MOST IMPORTANT, REPLACE EGR VALVE, IT GETS TOTALLY CLOGED UP, YOUR ENGINE IS KNOWN FOR THAT. I HAVE A GNC 2500, 3/4 TON. SEEN IT ALL. CHANGE YOUR DISTRIBUTOR CAP & ROTOR ALSO. JUST DO IT !!!!!!!!!!!

Without checking your car physically, its not possible to give you any idea what it could be or not

Engine stalling and rough run issue at low speeds

This problem is commonly caused by a dirty automatic idle speed control valve and throttle valve. Buy a can of throttle valve cleaner (do not use carburetor spray cleaner!) from NAPA or Carquest (made by CRC chemicals) and spray it into the air intake while the engine is running, use up about 1/2 the can, engine will try to stall hold the speed up, shut it down and let it soak for 30 minutes, restart and blow out the remaining fluid, shut it down and disconnect the negative battery cable for 5 Min's to reset the base idle control

That would be your engine "choke" functioning. It's not a problem. The choke engages when engine is cold and shoots extra fuel to the cylinders to idle the engine up especially in cold with. Once the engine has sufficiently warmed up, the engine will idle back down.

Maybe a short to the TPS or something shorting it out. There's also the IAC that really controls the idle but usually it will cause the RPM's to go up and down a little erratic if bad. The MAF sensor can cause major problems as well but since you already swapped the TPS and it helped and then stopped I would focus on that sensor and especially it's wiring to and from the ECM. Be careful with the sensor signal wire to the ECM can blow it if more than 5v passes or spikes.

Does the oil light come on or the knock occur during the engine warm up after a cold start?
There could be a couple of problems causing the issue. You could have an oil pressure pump or pump pressure regulator sticking. I would have a mechanical oil pressure gauge installed and verify oil pressure at idle and 2500 rpms to make sure oil pressure is in normal ranges.
You could also have excessive piston rod bearing, crankshaft bearing or cam shaft bearing wear that will cause oil pressure to drop too low to prevent the rod knock your hearing at 2500 rpm.
You said a knock and not a ticking noise,so I don't believe a lifter is the issue at 2500 rpm.
Start with the oil pressure check and go from there.
Let me know.
Regards,

Sounds like you have a vacuum leak in the air intake side. Check all your small and large hoses around the throttle body. Also check your idle air valve....cylindrical device connected to the the air box at the front of the engine.