Ok, have a 1999 GC with the 4.0l 6 cylinder. After warming up, when you come to a stop light and sit for a little bit, then engine will shudder, RPM's will drop about 50 to 70, the voltimeter will drop a little, then everything will return to normal. Engine seems fine while driving, no loss of power or hesitation.

Had the fuel pump and plugs replaced about 6000 miles back. Tech said the throttle body was dirty as well and cleaned that. Problem did not occur for awhile after the throttle body was cleaned. Why would it get so dirty so fast? Or is there something else we should have checked out?

it sounds like the Idle Air Control valve is bad or the port (which is located in the Throttle Body) is clogged, I would start by cleaning the Throttle body ports, with some Carb cleaner or throttle Body cleaner.