Runs Horrible, Bucks Then Runs Awsome.

I have this problem where it would be like a stumble/bucking but this is the funny part my 88XJ would run horribly for the first 10-15 of driving wouldn't go if I hit the gas and it sounded like a 30 year old beat up V8 with crappy exhaust (usually on the way to work) and if I decide to hold it at around 2500-3000 RPM it would stumble then buck, usually bucking pretty hard, it's like something cut off the gas then in that same instant you get launched into the seat. After that it would run like a champ, tromp on it it would snap the speedo, plant you in the seat and sound like a built hotrod, like it used to and it would be fine ti'll it was turned off. When I start it up again same process again. The exhaust is new along with a new cat new wires, cap, plugs ect. Don't know what it could be.

could be alot of things.

bad fuel pump, regulator, and/or filter
bad coil or icm
bad tps
bad o2 sensor
possibly bad egr valve
bad MAP sensor


what have you tested so far?

bad fuel pump, regulator, and/or filter - Going to check those on weekend
bad coil or icm - Already checked that, it's good
bad tps - Not sure seems to be functioning normally though
bad o2 sensor - Would have came up in emmisions test, it was ok
possibly bad egr valve - No clue, could pick them up at the wreckers
bad MAP sensor - Not sure either, again, pick up at wreckers

I'm guessing that maybe it has something to do with my fuel. I was just thinking about that today. When I had my e-test done my pollution was very low, in all the tests it was barely registering in the green on the low side.

I'm not sure about the TPS. It doesn't seem to act up regardless of my throttle position. It reacts the way it should. The MAP sensor and EGR I'm not too worried about, I can go to the wrecker and get those. There's a Jeep in there with a freshly rebuilt motor with everything new. I think I'll yank all the sensors off that tomorrow.

I have yet the to change the inline fuel filter, maybe it could be the fuel pump or bad injectors. When I changed the plugs, cap and wires I checked the coil too, on top of that I even pulled the head cover and checked springs, rockers and the rods to see if they were binding or if there was any damage. Just today I dumped in some fuel injector cleaner, this seemed to be reacting to it. I was maybe going to go and get a another sending unit and pull the injectors off to inspect, prolly won't happen ti'll the weekend.

Got to get an oilpan too.. it's leaking like a sive.

try temporarily bypassing the fuel pump resistor. when those things get old they are crap. the ceramic insulator will crack and they will corrode and give a really shitty connection. also, check your vacuum lines. when it starts running badly, unplug the map and see if there's a difference. if there is no or little change, there's your problem!

Check your compression after you check all else.