TooMuch4You

Ok, so here's the deal. I start my car and it goes up to 2800-3000 for a few seconds like it always has, and then it drops down and holds at 1500 and holds like it always has (or when i start it in gear it just holds at 1500 like it should). The problem is that once the temp starts to come up, the idle raises slowly to 1900 instead of lowering like it used to. Even once the temp gauge reads what looks like full operating temp, the idle still sticks up there. After about 15 minutes of normal city driving, the idle will come down and sticks at 750 just like its supposed to, and the car drives exactly like it should. I'm thinking this is a problem with the warmup system because it is definately still in warmup mode while the idle is high (I can tell that the car isnt leaning out the mixture). I installed a new thermostat thinking that it must just be opening way to early but that didnt fix the problem. So here I am, help me out guys.