I need some help because this problem is driving me nuts. I have a 97 Jeeep Cherokee Sport with 4.0 and automatic. The problem is while cruisng about 30-60 mph if I let off the gas the RPM'S drop from 1500-2000 to about 800 and then bump back to around 1200 until i hit the gas again. I believe the problem has to do with the lock up and release of the torque converter. Has anyone else had this issue?

 

The drop in RPM while coasting is normal, however the bump back up to 1200 I don't know about. It has been awhile since I have driven a Auto vehicle with a lock up converter.

 

i have a similar problem. 87 renix 4.0 aw4. at 25-65 mph if i let off the throttle the rpms die down, but go back up 500 rpm, then down 500rpm. like it is confused wether or not it is under load/no load. im thinking of rigging up a little test light so when i drive and the torque converter locks up, it lights up. i also suspect the MAP sensor. or a vacuum leak.

 

Mine does EXACTLY the same thing. It has for the past 3 years. I've learned to just look over it, just one of those annoying little XJ things. Good luck fixing it, if so PLEASE post the cure!!

 

The RPM'S drop like a rock. It happens very fast not a gradual drop like normal.

 

Also the MAP, TPS, IAC, IAT, CTS, Fuel Injectors, Plugs, Wires, Cap, Rotor, and Coil were replaced. The Throttle Body was taked off and fulled cleaned and the TV cable adjusted. I also inspected every vacuum hose and took it into shop for a smoke test with no leaks found. I also did a compression test with very good numbers across the board as well as de-carbon the engine.

 

My manual was doing the same thing except when i was depressing the clutch. Turns out it was my o2 sensor

 

It should be normal to drop down to 800ish and pop back up to 1200. I only noticed it because I had a battery problem that led to stalling at the bottom of the bounce a while back. Engine sounds fine when it happens right? A guess would be the IAC (or whatever sensor is responsible) doesn't quite register the throttle being released in time to compensate.

If is not normal, what is the negative result of this? Kind of a coincidence the low end and high end of the bounce is what your low/high idle is.