I posted both these issue last year seperately and tried many of the suggestions offered to resolve the problem. As you can see, the problem still there. I'm just hoping maybe someone might have another idea that I haven't tried yet.
My 93 jag. 4.0 runs extremely rough/poorly when started from cold and as it warms up it gets better. When it reaches operating temp. it runs great off idle, but at idle still runs rough, but does not die.
I've replaced the cold start sensor, maf, air intake valve, new ecu, throttle body, took it into a shop that reset all the sensors to proper settings electrically (it ran worse after that), changed plugs about 3 times, checked and double checked wires and cap. Checked and double checked for air leaks with carb spray, and cleaned every engine sensor if I did not replace it. I'm at a loss for ideas. Anyone have a suggestion. I have doubles of almost all the engine parts, due to replacing everything.
It runs great off idle and starts up everyday.

 

Sounds like my '96 4.0 except it will die some of the times I stop at lights. Thus far I have replaced coils, plugs, Idle Air Control and the air filter. Going to think about replacing the TPS which is fairly expensive.
RagJag

 

Ragjag,

Try the EGR Valve. You can try cleaning it, or pay the $100 for a new one.

 

Already did the egr valve, cleaned, no change, replaced with a certified used one, no change. Also already changed the TPS twice, tested used ones and had it reset twice, no change. The 93 doesn't have coil packs, so I did not have to replace those. I truly appreciate the suggestions, hoping to hit on something soon.
Within the last week, I retorqued the intake bolts, replaced the ignition cap, again, replaced plugs with champion, then NGK, again, no change and today I'm going to pick up another set of new wires and try that. Thanks again for the suggestions and I know one of these days we will hit on the right solution.
I'm also looking at a new mechanic shop to take it to, but after spending a ton at the last one and basically having them do the some things I already did, I'm a little disillusioned with spending big money for no results.

 

I would check the EGR again. Remove the valve make a block off gasket and reinstall, check your idle.

 

Scotland,
So what your saying is bypass the egr valve all together. Wouldn't removing the vacuum line and plugging the valve intake to the egr do the same thing. I tried that before and it didn't make a difference, but I did not use a block off gasket. I will give it a try if you think removing the vac. line isn't the same thing.
I installed new ignition wires and plugs and no difference. EGR sounds like my next attempt. Thanks

 

Scotland, I do appreciate all suggestions, but unfortunately for me, I tried blocking off the EGR valve and it did not make any difference. I plugged the vacuum line, I tried it with the line unplugged/open, either way did not stop the rough idle. According to my computer printout from the last shop that worked on it, it appears to be running to rich at idle and at cold start. I changed out the cold start sensor and also changed out the computer to try to stop the rich running. Is there any other sensor that might tell the engine to run to rich at idle. I'M LOST FOR SOLUTIONS.

 

I'm assuming you guys have not been able to find a Jag shop with the old PDU equipment?
There is a place just outside of Washington DC that has one of these devices. When I bought my second 1996, it seemed to be the only way to reset a high idle I was experiencing.

I would have to recommend a search for a mechanic that has this old device. I won't be that easy, but with the Internet today, it won't be impossible either!

 

Unfortunately the PDU had a name in some mechanic circles as Pretty Damn Useless. It may not be profitable to locate one. I am getting the idea that the rich idle condition is pretty common to the 4.0. Still looking to find the problem in mine.
RagJag

 

I understand, but for some reason, I couldn't get the idle setting to be set without it.

It may be useless for the most part, but I believe there a few things it does that cannot be done using any other method...which is bad for us facelift drivers. It may have had its name derived because it didn't do many of the things it was probably designed, marketed and sold to do.

All in all, it was a $150 charge to fix a problem unrepairable by two mechanics who seem to be able to troubleshoot and fix all other issues, albeit mechanical in nature.

I wasn't suggesting buying one, just finding a shop that did.