Check the mounts as mentioned. I have seen cars with a weak spark do this only at idle. The way to find it is to buy a spark tester (a few bucks at HF) and check for a BLUE spark to every plug. A yellow or orange spark can be considered weak and cause a stumbling at idle that you wont notice on acceleration or cruising. If you do notice a weak spark, chances are you need a plug wire or a coil.

 

do any of the plugs look fouled ?

 

Wouldn't the OBD throw a code if the cats have been deleted ? I thought the rear O2 sensors monitored the cats. I'm just sayin' the OBD may not be working at all.

 

You just fool the DS o2, as long as the DS has a lower ppm reading it thinks there is a working cat, can be done using a couple spark plug anti foulers to get the sensor shielded from the gases

 

I had this Jeep with the 5.9L, may it rest in peace, that was doing the same thing.... light skip at idle, slight piffing sound in the exhaust (flowmaster, so sweet on that big motor) when #8 cylinder missed, but give it a little gas and get on it a little and it smoothed right out and ran great. Turned out to be a compression issue

 

Have good blue spark on all 8 no fouled plugs whats good psi for compression haven't got to the motor mounts yet and yes the cats are gone the obd shows no code also tried a snap on scanner on it it shows no codes it runs much better with out the cats and cooler is there a way to test the injectors ? And thx for all the suggestions ! Anyone know if theres a good place in indiana for a rover?

 

If an injector was not firing, you could find that with a NOID light. But that would definitely have thrown a misfire code. However, it could be a volume or spray pattern issue that is covered up by increased RPM and fuel pressure (acceleration). The only real way to check volume and spray pattern is by removing the fuel rail from the intake, leaving everything connected. Disconnect all but one injector at a time. Using a graduated cylinder, point the injector into the cylinder and crank for a specified time (that time would be in the FSM) and observe the amount of fuel dispensed (correct amount also in FSM). Spray pattern can be determined by holding a piece of cardboard under the injector (FSM specified distance) and observing the conical (or so you hope) spray pattern.

There's bits in the RAVE about leaky injectors too. Something about drips per minute or something. I didn't read it too closely. Worth looking into.