I have a 02 Eclipse GT and some times when I start it the RPMs will run well below 1k and the car shakes a bit and makes a rummbling noise after a bit the RPMs come back up and the noise goes away

What kind of noise? Care to explain? It's kinda hard to explain online, it's better to understand in person. I'd say take it to a shop. I'm not too familiar with the 6G72 but I have friends that may help you. I'm more familiar with the 4G63 and 4G64.

It sounds like your IAC may need cleaned or replaced. You may also want to test the throttle position sensor's voltage.

Its like a rumbling noise really I thinking thats the best way to describe it

does it cause a vibration to the car?

Does it do it when it is cold or cooler out? Had the same problem and it ended up being the MAP.

Yes it causes the whole car shake and it does it when its both cold and warm.

Try disconnecting the MAF at COLD startup. If it acts different and run higher in RPMs and stays high, it's the MAF. If it kinda does the same thing, try another route (like asking a friend for second opinion mybe a girlfriend, mom or female friend, btw women can mimic an problem with almost any car dead on).

if it is carborator just make sure that the carborator is clean and the car is enogh warm before driving if injection make sure that the injector and the fuel pump are workin properley

It's fuel injected. All Mitsubishi Eclipses never came with a carburetor. Usually the injectors on these cars last a while unless he uses Heet or some kind of injector cleaner in which I don't know why people use that crap and end up over "alcoholing" the fuel injection system causing wreck like leaking injectors, fuel lines, and fuel tanks. Not shooting off at you Ebrahim, just ranting over crap.

Nope I have never used heet or and other fuel injector cleaner.

You could try resetting the ecu.

Hmmm hows that done?

Unplugging the battery from the car for about 3-4 hours or over night. then start up and let idle for a while to let the car find or recalculate it's fuel trims. Idle for about 20 mins with (key in ignition btw, no keyless start) take it around the block a few times. Easy on the gas first, then kinda go heavy on the gas, then drive like you normally drive, so that the computer can relearn your driving techniques.

Alright I will give that a try thanks.

might be that your maf sensor just needs cleaning or a bad vac