help car is broke

i have a problem with my car usually in the mornings not all the time but usually when i start the car it dosent idle right and if i give i give it gas and it spins less than 2,000 rpms it dies and also when i switch gears if i let it sit and worm up for a while it stops. i took it to a mechanic and they asked me if i took something off my ecu when i changed my air filter which i dident they "fixed" it and it ran right for about 3 days then i put a cold air on it and it started doing it again i think it has something to do with my throttle body or my oxygen sensor but i dont know i just recently started getting into cars i cant find anything anywhere about this problem any help would be apreciated.

its a 96 eclipse

and Eclipse what?
mods?

My eclpise does the same thing. I have a 91 fwd 1.8l with a manual tranny. I read that the ecu determines idle speed, and so its pretty much reccomended to try and not adjust the idle. So I guess we need to find out what the ecu looks at in order to determine the idle speed. Does it look at the coolant temp sensor, how many more things??

My Eclipse 91 2.0 does the same exact thing i was told u might have a vaccum leak somewhere so i just recently changed all my old vacumm hoses with new ones and until my tranny comes back from the shop i will not find out if it is fixed.So ill let you know if it fixed it i do know that all of my hoses were leaking and be aware of the fuel pressure regulator hose becuz i think that might of been the problem but i wont know for a week when my tranny comes back