Can anyone help me out?...I have a 99 Jeep Grand Cherokee 50k miles and I am having issues with vibration in the drive position when I am not moving...I noticed that the RPM surges from .7 to .6 which is causing alot of vibrations felt inside the vehicle..When I turn on the compressor the RPM moves up to .9 which elimates the surging and is much smoother...However without the compressor on the RPM continues to surge up and down...Anyone have a clue? I just had the throttle body cleaned, fuel filter cleaned, ail filter replaced, and spark plugs replaced..Any ideas Anyone?

I have this same problem. If you hear anything that would be great! We were told it was a dirty engine, paid for the work and it didn't work!

I heard someone mention an Idle sensor...Not sure though what that is and if it would make a difference...

The idle sensor is located on the trans bell housing. It is exactly spaced a certain distance from the housing, and if loose, could move and cause ignition problems. More likely, it is goig bad. Replacement is fairly easy since it has a cable that plugs in to the harness; part less than $100.00. Check this out before spending big bucks on other diagnostics.

The same problems exists on all Jeep models. Go here.
Jeep Idle Sensor explanation (http://www.off-road.com/jeep/cherokee/xjtech/engine/40ltr/tdcsensor.html)

I heard someone mention an Idle sensor...Not sure though what that is and if it would make a difference...

HI, THE AIR IDLE CONTROL VALVE IS MOUNTED ON THE THROTTLEBODY, IF YOU REMOVE THE RUBBER AIR FILTER HOSE AND LOOK INTO THE THROTTLEBODY YOU WILL SEE A SLOT INSIDE.THIS SLOT WORKS WITH THE IDLE AIR CONTROL VALVE. IF THE INSIDE OF YOUR THROTTLEBODY IS DIRTY , NOT SHINY YOU NEED TO CLEAN IT. THE POST ON THE IDLE SENSOR , THIS IS THE CRANKSHAFT POSITION SENSOR, HAS NOTHING TO DO WITH IDLE, THE CRANK SENSOR IS MOUNTED ON THE BELLHOUSING. IF YOU DON'T HAVE SPARK AT COIL WIRE THE THIS IS THE SENSOR YOU WANT TO CHECK. THIS INFO IS INCORRECT, HAS NOTHING TO DO WITH IDLE. EMAIL jeepman600@aol.com will send you info dale :screwy:

Had the same problem with my 96 JGC 5.2 Cleaned the throttle body and replaced the IAC.Problem Fixed.