Engine problems

Ok heres the deal I have an 88 xj 4.0. The problem is this. It started with the fact that I would start the jeep it would jump to 3000 rpms and stay there tell I shut it down. I would restart it and it would go up to 2500 for 2 to 3 seconds and then drop to idle. 4 days ago I became aware that it now would have a short loss of power you can feel on coast. Then sunday afternoon all hell broke loose. It started jumping and bucking and searching for idle tell it would die at a full stop. I got it back home and have sence tried replacing the map, iac, tps, o2 all at the same time with no luck or change. Now it wont even idle for more then 30 seconds before the iac opens full and then it starts to shake and the rpm's jump to 2500. If I open the throttle plate up it moans with little change in rpm the if I let go of the throttle it dies. Tonight T removed the igni. control module and had it checked by autozone it failed on all levels except the lamp. So i replaced that and still no change. Any idea's would be helpfull. By the way on sunday while nursing it home it would buck and spit untill the rpm got high enough and then it would accel. Up to speed. If I backed down to coast it would buck and loose speed. By pushing the throttle down more and uping the rpms it would smooth out and accel. to the speed I wanted.

Im stumped and need help

Check over your EGR system very closely. I did have a similar problem on the '89 I used to own and it turned out to be the vacuum switch on the left fender that controls the EGR valve - held the valve open all the time which translates into a massive vacuum leak at idle. Unplug the vacuum line on the forward side of the EGR and see if that cleans things up. I believe there was a discussion last week on the OEM tech forum that turned out to be a dirty valve that wouldn't close all the way. Try to clean the valve and get it to work before buying a new one. I think they are still mega-expensive. The high revs at startup may indicate a CPS that is on its way out, but get the main problem solved first.

Before anyone else says it - this should be in OEM Tech - NOOB:roll: :roll:

EGR has been disconected from the thermal switch, and caped off at the check valve inlet. should I remove that and cap both lines independently or leave the check valve alone.

Hard to tell what you have left of the system. You should have the EGR valve itself mounted to the intake manifold with a large pipe going to the exhaust manifold. Just forward of the EGR valve there should be a vacuum transducer (flat, black disk with three vacuum hoses). One hose goes to EGR valve base for back pressure sensing, one goes to the EGR valve diaphragm, and the other goes to the EGR solenoid valve mounted on the fender. Now that I refamiliarized myself with the system, I recall that my problem was with the transducer. It has a diaphragm in it that is supposed to bleed off the vacuum when the backpressure is low (idle and I believe coasting) so the EGR will close. Mine had a bad diaphragm so it would never bleed off the vacuum and kept the EGR valve open all of the time. This was confirmed by simply disconnecting the transducer which immediately solved the problem. I got another transducer at the boneyard that gave me a permanent fix.

It sounds as though parts of your EGR are missing or have been defeated leading me to believe that someone has been trying to bypass the system rather than fix it. Or it may have been a misguided attempt to improve mileage. Anyway, make sure that the pintle in the EGR valve is clean and is completely closing. And if you have the rest of the system, hook it up and make sure it is working.

Other things to check: Make sure all of your electrical grounds are solidly connected. The most common ground problem is the braided wire that runs from the firewall (passenger side) to the engine block. There are others that I don't remember locations of, but search on this forum and you should be able to find several discussions. Another problematic connector is the C-101 connector that makes the transition from the engine compartment to the interior. The contacts get corroded and must be cleaned with contact cleaner and then sealed with dialectric grease. I never experienced it but there should be lots of threads about this one too. Since you've been jumping and driving through mud, make sure all electrical connections are clean and intact.

I'll give you a call tonight and see what progress you're making. PM me a email address and I'll send you some stuff that might help.