Hey all working on a friends 2001 Jeep Grand Cherokee 4WD with 4.0. I checked codes and replaced the crank and cam sensor. Now after all that it is giving a weird idle under 1000 rpms it will be like a surging idle but not constant all the time. Sometimes will stall and die but start right back up. It was throwing 1391. The counterdrone at Autozone tells me the timing chain or timing belt may have jumped causing the code. Once in higher rpms seems to do fine. Oil was just changed as well. Any input to the issue will greatly help me get rid of this vehicle which has been a headache.

 

There are a lot of things that could cause symptoms like that a few are:vaccuum leak/clogged fuel filter/bad pump/bad injector/upstream o2 sensor uhh throttle position sensor...thats a bought all i can come up with of the top of my head...oh or a bad distributer cap or rotory button

 

My sport use to do the same thing. I replaced the PCV Valve and it went away (Positive Camshaft Ventilation Valve some places list it as a PVC Valve for some reason). It is a little elbow on the back of the valve case. it gets clogged with oil that get forced through it with the blow by. It should be the same for your jeep since its the still the same motor.

My jeep would surge and die if i took my foot off the gas when coming to a stop. It would also run rough at idle. It only cost me $15.95 to replace Hope it works!