Stumbling on acceleration, very strange dsm

[spocks90talon]

ok i just put a new ecu in my 91 gsx, new caps completly rebuilt the whole deal, the car ran awsome the first week but last night i was leaving my friends house and it started acting wierd, i had it in 3rd going about 25-30 and all the sudden it started hesitating like it was missing or something, i hit the gas a little bit and nothing the rpms were just going down like like i wasent hitting the gas at all so i hit it a little more and at about half throttle i finally got some response. so i started heading home hoping and praying that it would make it home, it continued to hesitate like that every couple minutes, i found that if i down shifted it would go away for a little while but start again after i picked up some speed. i got it home so i started doing some tests, the ecu is brand freaking new so i dont think thats it, i tested the plugs, wires(which are less the a month old by the way) i tested the coil and power transister, both tested fine, the checked the fuel pump(walbro 255) seemed to be working fine. no check engine light. now there is a couple things wrong with the car that i know about but i wouldnt think it would cause it to hesitate like that, my themostat it messed up it doesnt open all the time and one of my downpipe bolts is loose, oh and my radiater fan hasent been kicking on latly, i havnt been overheating really though, it runs a little hotter then it used to but never goes past the mark on the temp gauge. i drove it to work this morning and it was hesitating like it was last night, but this time at idle it would lope(rpms go up and down) and if i hit the gas it would go up to about 1500 rpms and start to lope again, the rpms wouldnt go above 1500 in neutral unless i hit the throttle past half way then it would rev fine, once the car was in gear it would rev fine it would just hesitate like i described above. now for the weird part, when i drove my car home today it ran perfectly fine! no hesitating, no loping idle, no nothing, it ran like it should(like a bat out of hell ) i didnt boost it really because i dont want to make it worse but it drove home about 2-3 miles perfectly fine. this has me very very confused does anyone have any idea what could be wrong with my car? i am fairly positive its gonna happen again, i mean the car cant just ran like shit one day and perfectly fine the next when i never did anything to it! of course it is a dsm so maybe ill do some more tests and post again tonight. thanks guys

 

[jdhutchin]

Maybe the throttle plat e is sticking? You could try cleaning out the tb and make sure the throttle cable moves smoothly.

 

[spocks90talon]

really no one else? i checked the trottle plate, it moves fine. i havent been driving the car but yesterday i started it up and it seemed to run fine, i kinda wanted to figure out he problim before i started driving it again, one buddy of mine said it might be a bad engine ground so im about to go check all those, ill post back later

 

[Smevans]

I came on today looking for solutions to the same problem. Mine occurs when I'm on the highway, when I restart the engine it goes away. I never have any problems in the city but when I head out at over 100km/h it starts to do it after a while. Help us both please.

 

[spocks90talon]

think i found the problim, it was a bad ground to the igniter, i changed the ground location and it hasnt happend since

 

[92GSXBaltimore]

i had the same problem and it was my CAS.