anyone got any ideas as to what it might be at a idle it sometimes is rough and other times not but while driving its smooth

 

id check for vac leaks, inspect cap & rotor, spend 15 bucks & replace plugs. if all check ok,id seafoam intake. good luck to you.

 

i had this exact problem, check your motor mounts. easy fix and cheap. easy to tell if they are bad to.

 

usually the drivers side will go first. replace them both if one is bad

 

My throttle body was all gunked up.. I cleaned it really good and it smoother out my idle.

 

thanks i already went and replaced the plugs wires cap rotor and did a oil change so i will check the mounts when i get home

 

Clean Throttle Body, IAC, TPS. Check pressure regulator.

 

I also had motor mount issue. Didnt know until motor took a nose dive into radiator..not fun. Mine was welds though.

 

I have the same problem. I have replaced everything ignition wise. Ran Seafoam 3 times in the intake, and (3) 16 oz cans in 3 straight fill ups. It idles better, but not like it needs to. I think i am looking at a head replacement. i also have a so so compression in cyl 4, BUT, I get a misfire code for cyl 1, never for 4..... WTF? This winter I am going to R&R my head, need to replace my exhaust manifold anyways.

 

Does the 4.0 Cherokee engine have an egr valve (like my S10 Blazer)??

If so I've had several experiences over the years on one 4.3 V6 where pieces of carbon get hung in the egr valve and cause rough idle issues. Nothing fixed it, not the GM "upper" foam cleaner, not brushing out the passageways, not replacing the egr. It lasts awhile and then comes back (it'll go away when I sell it)