94 Cherokee 4.0 5 speed..starts fine, idles fine about 800 rpm..no check engine light...when cold runs good. after driving awhile it will buck and studder like the rear end is tearing apart. unless you stomp on the gas. Hitting a bump in the road will start the process too. changed plugs, wires, cap, fuel filter. don't know what to look for. please help..tks

 

The fact that it runs good when COLD makes me suspect of something happening when the engine gets into "closed loop".

Oxygen sensor is a possibility. Data from the O2 sensor isn't used during open loop when the engine is first started, but it doesn't take long before closed loop is achieved and the O2 sensor is a player.

Do you know how many miles are on the current O2 sensor? They have a lifespan of between 100k and 150k, depending on the efficiency of the engine. And a faulty one can create bucking and stuttering. They aren't that expensive; if you purchase one, I'd get an NTK, which is OEM for your vintage 4.0 engine.

A faulty coolant temperature sensor can also give some strange symptoms as well. If it is feeding the computer with bad input signals, the computer doesn't know how to adjust for proper fuel/air ratio.

 

if the coolant temp sensor is the one in back of engine near oil cover I just changed that because my temp gauge was not working but it does now. just don't know what to do..tks for quick response

 

also had a crack in exhaust manifold about 6 months but just had a new exhaust put on this morning at repair shop....left there warmed her up some and it started that crazy bucking again...tks

 

That is the SENDER for the gauge, not a SENSOR for coolant temp.

Coolant temp SENSOR is in the thermostat housing.

 

Is there way to test that sensor? I have 2000 with same symptoms.

 

Replace the crank sensor. I had an issue with the engine missing and acting weird after hitting a bump on the freeway, it turned out to be the crank sensor. The only way I cought it was that I noticed the tachometer needle started to drop and act crazy after hitting a bump. New crank sensor and it has been fine for three years now.

 

Did you OEM replace the sensor through dealer or parts store grade?? Saw a much of posts leaning towards mopar grade

 

No, I used an aftermarket brand sensor that I got from www.rockauto.com .

 

I'm also having a similar issue. Starts and idles great at about 750 - 850. Drives fine around town, but if I get on the throttle too much, or let the rpms build, it'll start dipping around 2500 down to 2000 and back up really quick, and a lot. I've replaced the CPS, TPS, coil, wires, plugs, distributor pickup, alt resistor, and I'm at a total loss. Aside from maybe the flex plate got bent when I had it all apart for the rebuild, or the computer being bad, I have no other ideas where to look. 1992 cherokee 4.0