I just swapped the throttle body and now when I start the vehicle it idles at 4k rpm (so I shut it off immediately)

There is significantly more slack in the throttle cable now than with the previous throttle body.

 

Do the hard reset to re-calibrate the TPS.

- Disconnect both battery cables from battery
- Turn on ignition
- Turn off ignition
- Connect battery cables together
- Turn on ignition
- Turn off ignition
- Reconnect battery cables to battery
- Start the car
- Let it idle for about 10 Minutes

(Got your radio code? )


David

 

Thanks, wouldn't touching battery cables together short some electronics?!

Not supposed to need a radio code for US, how can I verify my radio is in US-setting before I do this?

 

Shortening the electronics is what you want to do!
That way you clear all the memory of the car.
After reconnecting the battery there will be a learning procedure that includes various re-calibration processes.

Do not shorten the battery itself, just the (unhooked) battery cables!

To set the radio to US region simultaneously press the AM/FM button and the tape eject button.
This will get the radio in set-up mode.
On the number pad, cycle through the different world regions using the 0 button until "US" is selected.
I don't know if that will disable the code though.

HTH!

David

 

The fact that slack changed at this exact time raises a red flag for me. Depending on how much slack, it almost sounds like the throttle may be in the partial open position. I would verify all linkage and cable connections are correct also. Just another thought to consider.

 

Did what David recommended (both battery and radio actually) and the problem still persists.

I think what SuperSport said is the issue - I watched the tach and it is not actually flooring-it but rather holding 4000 rpm, if I hit the gas it will roar way up to about 7000+ and then settle back down to 4000. Add the excess slack and it sounds exactly like the at-rest position is partially-open throttle. Any way to adjust this on the throttle body?

The throttle body company already offered to send me a replacement unit, but I would rather not wait for it to arrive and then have to do another TB swap - it took 2 hours to get this one in, there are a bloody-lot of hoses, wires and connections on this thing!

 

I have not replaced the throttle body, nor have I adjusted the idle, but I just walked out and looked. I hope these pictures make sense. I'm leaning over the Driver Side fender taking these. It's a North American car (Left Drive). First photo is for reference of where I'm looking, second shows as close up of the adjustment screw as I could get. It's done from the bottom up, so not sure how easy it's going to be, but that's the adjustment I saw.

 

SuperSport, you rock! I did install this with someone else, so it is possible that they attempted to lock-down that screw but are you 100% sure that it adjustments the throttle cable position? If so, how do I know when I have loosened it enough (and not too much?)

 

Again, I have not done it on THIS car, but I can see that the screw pointed to moves the throttle position when resting. It's not the Cable Position, but the Throttle Idle Position. Cable adjustment is done on the cable itself.

I don't know for sure if that's the issue here, but it's easy to find out. Start the car and SOMEHOW get a screw/nut driver on that screw. Adjust it out and see if the idle lowers. If it does, then that's it. If it does not, keep track of how many turns you've moved it out and put it back in.

If it's too hard while running, turn it 1 turn out when engine off, then start it. If your RPMs are lower, then that's it.

 

Ugggh, unfortunately my throttle body looks nothing like yours (probably because you have a pre-y2k supercharged and mine is '02 natural-aspiration.) I examined the old unit that I removed and there is no obvious mechanism for adjustment... Oy...

 

So, yours doesn't look like this? I just eBay'd it and this came up for 98-03 normally aspirated. Unless I'm seeing something wrong, it really looks the same as my 99 SC. Of course, eBay is not to always be trusted, as I've found out the hard way a few times...

This photo clearly shows the adjustment if it's at all like yours.

 

No such screw, my casting-series is 9E926 which is an air-assisted model, the best photos I can find of it online is:


(yes, I realize that the pictures are in the wrong angle to see the lack of adjustment screw, but I assure you it is not there)

 

Found a better shot: (note: plastic on mine is not cracked like this)

 

Funny, I've been searching for more pics of yours and I just found this photo also, along with others. I'm lost as to what to tell you. I'm sure one of the more experienced techs have done your throttle body before.

It seems strange though, as there's normally an adjustment somewhere. Especially, again, because your cable is lose where it might not have been before the change out.

I'll keep searching for an answer and post back if I find anything.

 

This is the newer style throttle body w/o a vacuum unit.
I have the same in my 99 XJ8.

I don't know how to adjust the idle rpms on this TB either.
The trottle position sensor can be adjusted (turned) so my guess is that this is the way to adjust idle rpms.

But be careful messing with the TPS!
When I tried to adjust (turn) the TPS on my XJ8 I got a "bang" in the drivetrain following a "transmission failure" message on my test drive.
So I set the TPS back to it's original position.

My initial problem was different though.
I had no high idle and no problems on startup.
What I had (and still have) is that my Jag is not decellerating properly. When I lift my foot off the pedal the car won't slow down as I'm used to from other cars. When I go for example about 30mph and let the pedal go completely (foot lifted off the pedal) the car still holds that speed and slowly, very slowly decreases it's speed.
It takes about 1/4 a Mile to decrease the speed from 30mph to 24mph (plain road).
So I feel that I do brake a lot more than I should. Not good for the brakes, not good for the gas mileage.
Idle is fine though (~600 rpm).

When I turn on the ignition I can hear a constant whine from the servo motor that turnes/opens the butterfly.
I checked the butterfly position with ignition on (engine not running) and noticed that the butterfly is always a bit open (a gap can be seen).
When I turn off ignition, the butterfly closes completely.
That was the reason I messed with the TPS.


After setting the TPS to it's original position I had the car in the shop.
They hooked it on the tester, testdrove it and told me that everything was fine, which I doubt.
But what can I do?

David

 

BTW...

Here's a thread about getting the slack out of the throttle cable to (re-)gain 100% WOT.

https://www.jaguarforums.com/forum/s...ad.php?t=38663
(See page 3 for XJ pictures.)

On the XJ8's there is a black plastic square "nut" secured with a zip tie (!) that can be popped out and turned to adjust the slack in the throttle cable.
Just be careful not to tighten the cable too much.

David

 

@ DavidN - the engine ecu might require an update in firmware? If a later throttle body is installed, I doubt if the engine ecu for the earlier TB has the correct setup maps.

 

I thought of TPS also, except that wouldn't physically hold the throttle open, would it? Have you looked down the throttle body to see if it's actually open a little?

Man, both of you guys problems are not good. As we all know, these motors are quite strong, so adding extra power when trying to hold it back w brakes is a scary thought.

 

When I adjusted (turned) the TPS I watched what is going on with the butterfly. (Ignition on, engine not running.)
Turning the TPS in one direction opened the butterfly, turning it in the opposite direction closed the butterfly (whining from servo motor stops).
I assumed that the butterfly had to be fully closed with no throttle so I put the TPS in that position.
Testdrive - "Bang" - "Transmission failure".
So I set it back to it's original position (with a slightly opening + the constant whine from the servo motor).
As I wrote - Shop said everything fine. Idiots... (sorry).

David

 

David, what do you mean you "turned" the TPS? What exactly do you turn? Could you please snap a photo or describe it the location on the ones that I posted?

re: throttle cable adjustment held in place via plastic-tie, holy cow, I was sure a previous owner had messed with the car - really lame that it comes from the factory held in place like that, a simple screw in threaded hole would be the proper way to engineer this...