93 Capri Rpms Jump

ok this problem is pretty major, for about 4-5 months now the rpms on my 93 mercury capri have been jumping at random, it started out as not being a big deal only causing problems every now and then but it got more and more troublesome as time went on now its at the point that we cant drive the car more then one place a day. What we know about the problem is this, it seems to run fine the first place you go, driving fine the whole time sometimes if you drive it a long distance it will act up, mainly though, if we shut off the car and then start it back up it will act up then. the rpms jump all around at first and the car will start to slow down even if you floor it it will act like its not getting gas sometimes it will lurch like its trying to stop then if i am going slow enough it will stall out if we are going faster is usually does not stall out but it does still act up. like as an example we drive about 10 miles on the highway to go shopping and then an hour later we go to drive back and it acts up, it will act up more in the parking lot but once we are on the highway it kinda balances itself out. I looked up similar problems at first and got conflicting answers. I know a mechanic who says he thinks its a mass air flow sensor, other options i have heard are ignitor (ignition coil?), idle engine, and throttle control valve? i think that is what they are called anyway. I have no more real info about it besides when it is colder is SEEMS to run better but i am not sure if that is true or if i just think it runs better this is a big problem and i need my car because i am a commuter so plz lmk ASAP
besides this the only other porblems i have had with the car is an alternator belt problem every year or so i need a new belt.