The vcm revealed a check engine code #4 which I found on one site is 4 - FEEDBACK CIRCUIT FAILURE. (CATALYST VEHICLES ONLY)

I found one post on here that alluded to it being a o2 sensor failure.

Symptoms are as follows.
1. Power Loss
2. Rough/surging idle
3. Starts after 30-45 minutes of mixed driving.
4. Revs slow like the parking brake is on when in gear.
5. No odd smells noted
6. Goes away after approx 1 hour of sitting.

I would think that a dead o2 would just be a bit rough running at idle if that, normally I just see bad gas mileage and black exhaust tips.

So I'm leaning towards a failure in the Cat Converter or possibly the egr system as the real problem.

Feel free to correct me on the code as I'm not positive it is correct. Let me know guys need to fix my sick kitty for the morning commute.

 

AJ6 engineering lists it as Lambda (oxygen sensor) feedback (catalyst equipped cars), which I guess would make it a o2 issue.

 

Wish I could help here. But its always encouraging to know that someone is reading your issue!

 

Army,

Check the connections for the O2 sensor. Sometimes they can cause a false check engine code. Also check out all hoses associated with the air induction system for potential vacuum leaks. If everything checks out okay, do the sensor.

Below is a link for the Jag-Forum Ebook:

http://www.jag-lovers.org/ebooks/boo...php?Vbook=xj40

Pay particular attention to part 12.26 for Fuel Fail 26. Even though the code is for a later model XJ, the same informational trouble shooting applies. Hope you get a simple solution this evening.

Good luck.

 

All the hoses in the air intake are looking good as well as the vacuum lines I checked them as soon as I got home. The problem doesn't set in till about 30-45 minutes into driving so I'm tending to believe it has to be sensor related.

Looked through the 12.26 and it doesn't seem to fit. By the time the check engine light comes on and the engine starts running poorly I've been at operating temp for some time

 

On the way to work today it went 50 min before faulting out. Check engine 4 again as well. Looking at the o2 sensor, it's easily original equipment. With 112k on the clock, I'm going to go ahead and replace it, as it can't hurt. Will update once I locate the part and swap it out.

 

If the cats are going bad this could be the problem, they clog up and the pressure will cause the head to warp. There are two sets, one in thwe manifolds and another set in the pipes.You should check to see that they are flowing well,by that i mean disconect the header pipes from the exhaust pies and make sure they are passing exhaust freely.I know as this happened to my 90 xj6 and only found out when they did an emission check and the car was way to clean(no exhaust getting out of the tail pipes. Otherwise the car ran great.To fix i punched the cat stuff out of the headers and replaced the exhaust pipe cats and all was fine.

 

I forgot to mention i had the same check engine and codes, I think when the system gets hot and expands it clogs off the system.

 

o2 sensor replaced and all is well.