could it be a sensor of some kind?

hi, 94 Cherokee 4.0 5 speed..starts fine, idles at 800 rpm. runs great when cold after warming up it bucks and stutters like rear end is coming off also when hit a bump in road. have to stomp on gas. replaced plugs, wires, cap and fuel filter..don't know whats wrong. any help please...tks

Did you check the pcv or airfilter try cleaning the TB out sounds like its dirty

Any bucking, stalling, and/or backfiring should make one suspect an O2 sensor issue. What are your gas mpg's ? A sudden drop of 30-40% in you mpg's should also make one suspect O2 sensor issues.

You can test the O2 sensor function.

Tim_MN said:

Any bucking, stalling, and/or backfiring should make one suspect an O2 sensor issue. What are your gas mpg's ? A sudden drop of 30-40% in you mpg's should also make one suspect O2 sensor issues.

You can test the O2 sensor function.

Click to expand...

I agree!!!

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=oxygen+test

yes mileage has gotten worse. mechanic did diagnostic test and said it was running "lean" before he repaired my exhaust manifold that was cracked for 6 months. but it is still shaking at times not all the time after it warms up and when I slow down to a stop rpm's drop low..no stalling issues except a few times when I was turning a corner and I just popped the clutch and it started back up. just that violent shaking at times. tks

It is either damaged wires to the O2 sensor, a bad O2 sensor, or a bad O2 sensor relay that powers the heater in the O2 sensor. Also check to see if the 94 used an O2 sensor heater fuse!!!! IF the heater is not working for what ever reason in the O2 sensor, it gets cold at idle and the bad data to the ECU makes the engine shake as the ECU looses control of the proper fuel injection rate for closed loop operation. The sensors are hot enough at higher rpms, but need the heater at idle.

Oxygen sensor can absolutely cause the symptoms you are seeing.

Especially because you are not seeing it when the engine is stone cold, when the oxygen sensor is not in play.

Definitely check the fuse for the heater circuit, but consider replacing it with an NTK. They don't last forever....