Ok guys, long story short. had the throttle body on my 2003 XJ8 replaced last week. The car ran fine for exactly two days. Today, I called the dealer to get the radio code to reset my sound system but the code they provided did not work.
A friend suggested disconnecting the negative terminal on the battery and re try the code. Disconnected the negative terminal for 5 minutes and started the car.

The car idled at 2000 rpm before settling at 1500. Putting it in drive and releasing the brake makes the rpm to shoot up to 2500 and from that point on it is a struggle to keep the car stationary.

Any suggestions?

 

Get a cheap fault code reader, plug it into the diagnostic socket & see if any 'P' code fault numbers are showing. These can be cross-referred online to the Jaguar OBDII fault codes & should help pinpoint the area of the fault.

Or you could try disconnecting the battery again...

 

Does it make a very quiet ticking noise?
If you turn the key to position 1, floor the accelerator twice and then ( without touching the accelerator again) start the car, it goes into a kind of throttle idle relearn deal.
It'll start with high revs then try to find a good idle rpm.

I did it and it took about 10-15 mins until I was sure the car was done doing its relearn.
Allegedly if you hit the gas during the relearn cycle it goes quite mad and does odd things, similar to what you describe.

Suggest that you try setting it in relearn mode by flooring the gas twice in ignition position 1 ( ie on, but not yet started). Then just wait until it either stabilises or it becomes clear it hasn't helped.
Key thing is don't touch the gas during re learn cycle.

Cheers

Lincoln

 

Agree with above, try to disconnect battery again - I had some problems with high idle speed after disconnecting the battery and doing a hard reset when trying to solve my ABS problem - however it never idled as high as yours is....

 

Thank you guys.
I will not have access to a code reader until Monday but I will do that A.S.A.P.

Fishfool,

Should I pump the accelerator twice in key position 1 or 2 (just before start) Please confirm.

 

Actually I'm not quite sure anymore. It's definitely before cranking the starter. I thought there was only one setting before the engine cranks, but I'm usually on auto pilot when I get into the car.
If you like I can pop down and check.

Edit to say, I think position 1, put the pedal to the metal ( or lambs wool) twice, then during the system check part my car makes a very quiet ticking noise, then start, it'll rev to 1500, then gradually go back down. There was a post about 2-3 weeks ago with the same or similar symptoms.

Lincoln

 

Fish,
Definitely two positions before crank. Pos 1 can operate windows and radio, no lights in the dash. Position 2 starts the computer and the car goes through the pre start check with all lights in the dash on.

Can't find that post... can anyone help?

 

This is correct. The procedure needs to be performed BEFORE the "SYSTEM CHECK" appears on the cluster. IF (and I repeat 'IF') the TPS "lost it's mind", this will make it learn the positions again. You said TB was replaced recently,.....with a new one, or used, who did the swap, and there is a possibility that the TPS was fried/damaged during/before installation.

In any case,.....codes will tell what's happening.

 

Agree with Danielsand,
This is exactly how I remember it.
And obviously if you have a code reader then reading the codes is the first step.
If you don't have one, there is likely a shop near you will do it for free, and on a Sunday, unlike here, where everything grinds to a halt.

Lincoln

 

If you remove the inlet air trunking over the throttle body & turn the ignition key to position 2, you can watch the throttle plate moving when you press the accelerator-this would at least let you know if it's returning to the closed position at idle.

As basic OBDII code readers can be bought so cheaply now, it's worth having one of these very useful devices as there is such a large number of 'P' codes that the ECU can throw up at you on these cars-it's a very comprehensive monitoring system.

I keep mine in the glovebox...

 

Performed the suggested procedure at position 1 and cranked the car. The idle settled around 1200 rpm but the check engine light came on and the car went into the failsafe mode.

Putting the car in drive and letting off the brake makes the car take off on its own.

Very important to get the car working.

 

Had rather hoped that would fix it. Would have been a simple fix.
But as the other gents mentioned, these are complex cars with lots of systems. The Check Engine Light means something is out of the allowable range and the computer can tell you this, using OBD 2
So as mentioned get the codes read and take it from there.

Regards

Lincoln

 

So they changed the TB, hmmmm. I had a similar problem a couple of years ago, car would rev up to about 2,500rpm at idle. Took me a while to find the problem and it was a vacuum leak, the air intake trunking had a small crack in it. Stuck some tape round the crack and the car was good to go. I just wonder when they changed the TB did they just twist the air intake tube out of the way or fully remove it carefully ? It's worth checking it out. If you get the codes read and it reads fuel imbalance or something similar I would lean towards a vacuum leak.

 

The TB is a rebuilt unit and changing it solved the issue with lurching, sticky acceleration and the car going into limp mode. The car was giving P0121 code as well.

It was running fine after the fix until I disconnected the battery and re connected it. Can anyone think of a reason why disconnecting the battery would trigger this extreme throttle response?

Right now I am stuck 80 miles from home (in orange county) with no access to tools or any diagnostic device.

P.S : My mechanic thinks that it is a programming issue and the new TPS needs to be programmed to the car. Does anyone know of a mobile mechanic with the appropriate computer to do the re programing? Feeling extremely helpless right now that a 15 minute computer programming job is screwing up my schedule.

 

Hey LAcat--

I am in OC and would be happy to speak with you- Costa Mesa to be exact.

Take a look at your throttle cable and see if it is too tight.... A friend of mine has his stick after it was worked on and had quite a ride on the freeway.....

You can unscrew the black square to loosen the cable after you remove the zip tie just remoember to replace the zip tie before driving.

 

I am at a job site in Lake Forest/ Irvine area. I checked the throttle cable and it is not tight at all, actually a bit loose. The ride here was perfect and the issue didn't come up until the battery was disconnected/reconnected.

I just took it around the block and it seems that the throttle is leaning. Reminds me of a child learning to walk for the first time. It will start at 1500 rpm, go up then go down 50 or 100 rpm at a time, settle around 1200 but when I put it in drive and take my foot off the brake, the car takes off and the rpm reaches 2000 plus. A wild ride to say the least especially on wet roads.

Do you know anyone locally here who has the computer to re-program the new TB? After talking to my mechanic and doing some online research, that seems to be the issue. My mechanic thinks that disconnecting the battery cleared the computer and now the computer is not reading the new TPS correctly because it does not "belong in the car".

I would highly appreciate your help.

 

I do all my own work, so I do not have a referral for you- I do know of a place in Costa Mesa but can't vouch for them.

If you unplug one side of the battery, touch the contacts then replug- then start the car and don't touch the pedal at all for 15 minutes what happens?

I swapped out the throttle body on my XJ8 (along with the engine) and have had no issues after letting it idle and settle down at an idle.

I have a code scanner and would be happy to meet you at the car tomorrow to read the codes- It's only about a 15 minute drive.

When you disconnected the battery, did you change or move anything else? (intake, vacuum lines, breather etc.)

 

I have done the battery connect and reconnect 5 times and have started the car without pressing on the accelerator but the check engine light stays on as well as the failsafe mode. No difference in the idle problem either.

The TB was replaced by the mechanic and it did run as it was supposed to for 150 or so miles afterwards.

I will greatly appreciate your help if you can swing by tomorrow. I just bought the car two weeks ago and I am very unfamiliar with the systems. You may find an issue that I can't think of.

My name is Harris and my number is three one zero- 279-three 8 one four. Give me a call when it is convenient for you.

Many thanks in advance.

 

Resolved:

TPS was misadjusted at the rebuilders- battery was not disconnected during installation so the car was running off the old values until the battery was disconnected.
Incidentally, there was a white mark where it should have been, and when it was adjusted to the white mark all went well.

 

dsnyder586,

I would like to thank you publicly for your help. Your help in my time of need was a great gesture and if there is any time in the future that I can do something to payback, please don't hesitate to ask.

I am starting a new thread about it.