I have a 2000 jeep grand Cherokee Laredo. Its an inline 6, 4.0 engine. It has transmission problem for sure but here recently it has been idling extremely rough at a low RPM like its getting ready to cut off and the oil pressure drops when I'm idling as well. Any ideas on what it could be other then the transmission. The fuel pump has been changed twice already

 

Drops to what? The minimum oil pressure on the 4.0 is 13psi.

 

It drops 0 like I have no pressure at all. A friend said the oil pressure switch needs to be changed and that's could be causing the rough idle basically because the switch is telling the rest of the engine that its low even though its not. Does that sound right?

 

No, not unless the GC has some weird extra electronics the regular XJ Cherokee does not.

The oil pressure gauge and sender are literally just for displaying oil pressure. On a 2000 the engine doesn't consider oil pressure as an input for operation.

What I would guess is happening is that the poor idle is the root cause and the oil pressure gauge drop is the side-effect.

I would start by cleaning the IAC (Idle Air Control) valve and throttle body to see if that improves your idle situation. (cruiser54.com has a write-up on this IIRC - or do a search on YouTube and watch the video with the cute girl..)

 

You mention the transmission is known to be bad (I'm assuming this is an automatic..), This is due to wear and tear (age/mileage) or not? If it's wear and tear/mileage, then what condition is the engine in?

I get the feeling the Jeep is old and worn and if so the problem may be more serious than a dirty IAC or bad sensor - but I'm assuming, so perhaps some elaboration might help.

 

If it's not the idle air controller, then I would suspect the throttle position sensor. Like what's been stated, I think the pump is worn and just can't put out the volume needed at very low rpm.