91 mitsubishi eclipse idles way low around 700 rpm and shakes the car pretty good.?

[mike d]

when i put it in neautral it goes up to about a 1000rpm and theres still a tiny shake. I've had the car since 98,000 miles and it now has 175,000 and its' been doing this pretty much since i got it, but it has gotten worse over the years. I just had to get it smogged and it was having problems so I have just recently had a lot of work done to it. So to rule things out, these are all new and replaced: TPS, oxygen sensor, air filter, spark plug and wires, rotor and cap, oil filter. And i had the transmission replaced about 50,000 miles ago and it did this b4 then and it didn't change anything. I read on some mitsubishi forums about an idle air control motor system, but i don't know if that is my problem. And another thing is a lot of times when i start my car it idles a lot higher to begin with like at 1200 rpm which is about where it feels it should always idle but then after a minute or 2 it goes back down. Anyone's opinion would be greatful. thank you