Jeep Cherokee Not Starting/Starting Rough?

Hello, I have a '95 jeep cherokee xj straight 6, 4.0 litre high output motor. Last winter it started behaving really peculiar, and starting rough, this problem continued to grow worse and worse untill now when it starts.... sometimes. By rough starting i now mean that i have to turn the key and wait for 5 to 15 minutes depending on how cold it is out side before the computer even turns on and engages the fuel pump, I know it isnt my fuel pump because i replaced it just a month ago and my fuel rail has plenty of pressure. Once the fuel pump engages the check engine light goes on and stays on for generally 2-3 seconds once it goes off the jeep tries to start but usually fails if you don't wait for the light to go off it doesn't try to start at all. By tries to start but fails i mean it fires for about 3 seconds and dies instantly. And so now you thing it might be a throttle position sensor but it isn't because i also recently replaced this. So then i usually try starting it giving it some gas this sometimes kindof works and sometimes it fails like before. By kind of works i mean that the jeep starts really rough and goes through a cycle of high rpm around 2000 to very low rpm around 500 if you hold the gas for about thirty seconds and then rev it the jeep usually will start tto idle on its own but lately it hasnt been and anytime you let off the gas it dies as if it doesnt want to run at all. Sometimes it doesnt want to idle after about thirty seconds of holding the gas and so i let it die and start it again without gas and it usually starts fine. The rough starting has not just been happening when the engine is cold too, it happens when my engine is hot (which if you believe the guage is about 210*, too hot?). Just yesterday i disconnected the MAP sensor connected to my airbox and the jeep started instantly reved to about 1500rpm and settled down to about 750rpm i was satisfied with this and this morning i decided to see if the same thing would happen when the engine was cold to see if it was a bad MAP sensor but this morning i got nothing, as i said it usually starts eventually, this morning i got nothing it didnt want to run or start at all i got it to fire 3 times in 15 minutes two times it died right away despite having the pedal on the floor and the third it ran, with the pedal on the floor, for about 20 seconds of which it backfired very loudly about 6 or 7 times, backfiring is not uncommon but it is usually only once or twice not this many times. also in the last week it has been idling very low around 500rpm and yesterday when i finally got it started it ran so low that my rpm pin was settled at 0 and read nothing i could hear the fuel pump going and the car shook. I also recently replaced the starter solenoid and mixture control solenoid as well as my throttle body assembly. The exaust has smelled very rich which is the reason i replaced the mixture control solenoid. Another problem is my computer doesnt remember problem codes. A couple times codes have shown up so i drive it home turn it off and test for the code but it says the engine is clear and nothing is wrong. The last thing i noticed was a large dent in my exaust right off my headers and just before wat i believe to be the oxygen sensor would this have anything to do with it. My jeep has just over 200,000 miles on it i love it, i recently put a 4.5" lift a new bumper and a series of offroad driving lights and fog lights on it it looks very nice if only it ran as nice as it looks, any help would be greatly appreciated i will be attending college soon and i do not have the money to keep throwing solutions at it. Please let me know if you have or have had this problem and what has or hasnt worked for you and if you have any suggestions.

Thanks,

Cassidy

yamaha125@wi.rr.com