here I come to save the day!
Hint: it´s not the throttle body.
It´s actually a thing called the Bypass air valve. It´s a valve that redirects air into the intake manifold and does so by using a thing called a "thermo-valve" which is an apparatus threaded into the coolant jacked in the cylinder head that will open and close due to temperature variations. When you car is cold, it will contract and hold the valve all the way open, giving you that high 2500RPM period. Then as the engine warms up, the valve warms up and starts closing, giving the lower RPMS. What happened is that the thermo valve is worn out or gunked up and is sticking during warmup, which is why it takes so long to get to that idle speed.
the reason why it´s called an air bypass valve is because it BYPASSES the TB altogether, why is why even though the TB butterfly valve is closed, the engine rpms can still vary through one of 3 things:
2. ISC (idle speed control) solenoid
3. air bypass valve
just replace this valve and you should be set. If that´s not the problem (and it most likely is), then the problem could be in your ISC. Leaks aren´t the problem in this case. Not by the symptoms you described.
I agree with pimp_asscort_89gt, even though he is a piece of white trash
The problem seems to be in the ISC (idle speed control)/IAC (idle air control) solenoid. ISC and IAC are still the same valve, only that the IAC is the common term for the 1.9L engine valve, and the ISC is the common term for the 1.8L BP engine, even though they´re really the same purpose.
You can take this out and then measure the resistance across the terminals. This will let you know if the solenoid is fried and needs to be replaced. This solenoid is by the way controlled by the PCM and is designed to shift idle speeds when loads are put on the engine, such as your 2000 wat stereo or air conditioning.
hope that helps.