went I drive normal my 88 xj6 will shift right at 2k, however under wide open throttle it will shift around 3.5k...it wont go any higher under ANY circumstance.

In neutral, it will rev normal.

Any thoughts?

 

I had this problem intermittent.

How about your fuel and air filter? Ignition system look good? Throttle body open up all the way when the peddal is pressed?

I found I had a whole bunch of issues that contributed to it. Coolant temperature switch was bad, tps was bad, etc. However I think what was the real culprit was a bad throttle possition sensor.

It was full of oil and would get funky around 3v and jump around etc. Now that it is fixed I have the power the car should have. I have felt it hesitate a time or two after a cold start but it figures itself out quickly.

The tps wont always throw a chk engine if it's idle voltage is correct. Check to make sure it's set at proper idle range. My factory one was about .45 but the guys over at Aj6 Engineering as well as others say .6v is the correct idle voltage. It should then move smoothy up to about 4.5v as the throttle is opened. If it jumps around it is bad.

Check fuel pressure as well. It revs normal when not under load so it sounds to me like a fuel problem. Either fuel is not getting to or through the injectors like it should or another component is telling it not to. So I say check fuel pressure and tps.

 

Are your sparking plugs wet?

 

I'm a Jag layman but your symptoms sound familiar; my rev limitation seemed so precise like it was computer controlled but in the end replacing the fuel pump solved my problem (ref. here).

 

My dad has a 2000 xj8 supercharged and his car also had this problem, there was a vacuum leak between where the supercharges mounts, so i would also think that it has something to do with your air intake, if you put the key in the ignition and turn it on, but not starting the car, the computer might "correct" the problem, we did this on the 2000 and it usually worked.

 

I havent fixed it yet, however I feel like I am leaning towards the TPS. I cleaned the entire intake and EVERYTHING was oil covered...(expected with close to 400k miles)