Engine Stumble

Quick question for you guys: When my jeep is idling it does this weird stumble/stutter thing every now and then. It happens extremely fast and only every 10-15 seconds. It happens so fast that the tach doesn't detect any drop in idle speed, nor do my senses. It just stumbles as if something in the engine just hit something and it makes the whole car shake a little, but there is no noise besides the exhaust changing when it happens. Seems to do it worse when its hot out and the car is hot, and it doesn't it much more often when the A/C is on. ANy ideas. It's a 99 and the engine only has 10,000 on it, bored out TB, exhaust, and intake.

Thanks
marcus

The injectors do get hot, but what you're prolly seeing is the emissions stuff pushing the limits of lean -- just slowly reducing the fuel untill there's a lean miss, then kicking the mixture back up a bit...

sounds normal to me...