I downloaded the DIY instructions for cleaning the throttle body, MAFS, and part-load breather because my XJ8 was hesitating when accelerating from a stopped position -- unless I really kicked it. I didn't clean the part-load breather because I didn't want to chance breaking it, but I did clean the throttle body and the MAFS as instructed, and disconnected the battery to reset the computer. Now this things goes like a rocket off the line! I was amazed.

But, now it remains at 1100 RPMs when I come to a stop -- in fact, it's hard to come to a complete stop because the idle is so high. If I sit for a few seconds, the idle steps down to about 700 RPMs. As soon as I release the brake and press the accelerator the idle hops up again -- I can idle along at 25 mph, which seems a bit too fast.

I drove around for about 1/2 hour or so in varying conditions. Start/stop, freeway driving at constant speed, freeway driving with some quick accelerations (i.e. kicking it down to "passing gear"), and everything in between. The idle situation has stayed the same.

Should this be happening? Will the idle eventually return to "normal" or is there something I should do? Would cleaning the part-load breather solve my problem?

This car seems to have fixed itself! I let it sit for a couple hours and when I started it back up, the idle was at about 600 RPMs -- perfect for me. All's well with my Jag!

God I love this car!

LOL, good to see it was fixed

Oldmike, I'll explain something for future reference - when messing with the throttle body and doing hard resets - the throttle once cleaned and reset will do a recalibration test where it starts high then slowly closes the throttle until the ecu see's a near stall the rev's will drop until it almost stalls then settles on a new idle point.

I think you didn't give it enough time to do this recal, you must have just driven it. Next time let it sit on tickover and do it's own thing....... little knowledge without full understanding can be harmful.

Actually, before driving it at all I let it idle in the driveway while I put my other car in the garage, only a couple minutes at the most. Then while driving it I would stop, let it idle down, wait a short while (1/2 min. at the most) and drive off. After turning it off and re-starting it, it recalibrated itself.

The calibration takes at least 5-minutes or so sitting in park/neutral, I have done it 3-4 times when I replaced throttle bodies (trial-and-error, doh!) The engine sounds a bit scary while it calibrates, sometimes it momentarily roars and other moments is about to stall, but indeed this is normal and gets all smooth & quiet at the end.

Thanks -- I might try it again just for fun! I need a life....

If you want to get a bit more kick out the cat, try this: https://www.jaguarforums.com/forum/x...estored-38663/

It is worth doing, as it actually increases MPG because you don't have to put as much effort into pedal pressing. Mine is adjusted to such a fine point I only need to touch the pedal with my toe and the RPM will increase. I have 100% throttle opening when the pedal is in the carpet.

Thanks for the reminder -- I did read that entire thread a couple weeks ago, but I was on vacation. Now that I'm home....

I done that cable adjustment too, highly recommended for both throttle-response "feel" and increased WOT air-intake - just be 100% sure at the end that it is not too tight or you will raise your idle speed (as you would not technically be idling but always on the throttle.)

I'm interested to know how the ECU 'knows' the throttle body has been 'meesed with' - or is this idle recal always performed as part of a hard reset?

It uses the same system that Traffic lights use, so they know to change to red when you're in a hurry or running late! LOL

Computers are the Devil though, what they can do frightens me sometimes!

I'll email you those Triumph pictures soon, I just need to find the Memory Stick they're on.