driving me nuts! what else can it be?

[trampolinedude]

Ok, this is my first post here and any help would be greatly appreciated. I have a 93 grand limited 4.0 4x4 that has has a gremlin that driving me nuts.
so once the car is driven for 15 or 20 minutes and is really heated up and is put in reverse the idle dips down and car starts to shake. It does not do it when cold or in drive even when hot. The car runs perfect otherwise. The tranny in newly rebuilt and i have replaced the following:
plugs, cap, wires,rotor, map,tps,and iac sensors. Im about to pull my hair out trying to figure out whats wrong!!
P.s....no codes ever!!
PLEASE HELP LOL

[GrandmasterWJ]

Did your jeep do this before you changed everything?

[AndyZJ]

I'd think a couple things could be wrong. 1 is a bad mount, either motor or tranny. 2 is a valve body issue that the place that rebuilt the tranny should look at.

[trampolinedude]

Yes it did it before all this was changed. That was why I initially changed all the maintenance items and sensors but it did not help. Then I rebuilt the tranny and have had it back at their shop 3 times but nothing changes each time. Also there is a small vibration when slowing down that occurs between 20-15mph...don't know if thats related but i thought id throw it in there?

[trampolinedude]

I should also mention occasionally the car surges and "bucks" when its cold or just "cooled" for a while. Does that for the first few take offs then smooth. i have disconeccted the o2 sensor cause i thought that might be the surce of my prob but it did nothing.

[96sdgc]

same problems ... that lurching is frustrating... i have tried a new IAC, TPS, plugs, O2 sensors, catalytic converter, dieting, refinancing my house... i have no clue what will help

[Technohead]

How about an animal sacrifice?

Its seems pretty clear the problem is tied in with the transmission somehow. What about speed sensor or something like that? Not sure if they would throw any codes or not.

[96sdgc]

i am not very fond of my dog right now... i will let you know how it goes.

[96sdgc]

recently sold the jeep that had this problem and went to a beautiful 98 with its own problems... but the guy fixed it with a bottle of throttlebody cleaner... over four hundred dollars of my money wasted and he spent 6 and fixed it... i guess you idle the vehicle with the thottlebody exposed and spray small amounts of cleaner in until the motor bogs down almost to the point of dying. use the whole can and when you are almost out of cleaner just unload it all in and kill the motor. let it sit for a few hours and take her for a drive.

[warren.bell]

Hello Trampolinedude:

Another thing this could be is a small vacuum leak. I had a similar stalling out issue on my 1993 4.0L ZJ. Since the brake booster is vacuum I would notice it when at a full stop applying brake. As a simple test, when you are stopped and idling with the Jeep warmed up and in park, just apply the brake. See if your idle drops. If it does, try replacing the hard plastic vacuum lines. They tend to get brittle over time and easily crack in ways that aren't all that easy to spot. This would also seem to fit with your "vibration when slowing" symptom.

Also, as suggested earlier, it's a good idea to check the intake for build up that could make it stick. This makes smooth transitions more difficult and these issues are more noticeable at lower RPMs.

Also, both of these issues are easy to test for and cheap to fix so I hope that's it!

Thanks,

Warren