I bought a 1995 Jaguar in January of this year and sometime around April it developed a high idle (1300 rpm in park/900 rpm in drive). I sort of put up with it for four or five months until it bugged me enough to try and find a solution. So over the last two or so months my car has been at two separate mechanics for around a month each and they have both failed to rectify the problem. Both of them should know their stuff as one is a general European prestige car mechanic the other is an independent Jaguar mechanic.

The first mechanic I took it too agreed to return the car to me after I explained that I needed the car and that nearly a month without a definite diagnoses was too long. The second mechanic to look at the car more or less threw in the towel after over a month. He offered a workaround solution which was to set the IACV to the correct distance for when the car is warmed up and then disconnect it. So basically on a cold start it has a slight hesitation and idles a bit lumpy until it warms up and then it runs fine. This isn't so bad as I'm in Australia and it's quite warm but it obviously is not ideal.

Here is a list of all the things carried out by both mechanics as they were written on the invoices in more or less chronological order:

- Checked for vacuum leaks
- Replaced IACV
- Replaced Coolant Temperature Sensor
- Replaced throttle body (I was told that the throttle return spring had also been replaced with a stronger one after I enquired about the TSB recommending this)
- Reset ECU
- Checked injection timing & fuel pressure
- Replaced rochester valve
- Replaced fuel pressure regulator
- Checked reading from TPS and stepper motor at ECM
- Tried another ECM
- Set throttle butterfly air gap
- Replaced TPS

It must be noted that each mechanic got to a point where they thought the car was fixed and called me up to come and collect it but when I arrived the problem had returned.

I'm not the most mechanically minded person around so I'm not really sure where to go next. The only thing I've seen mentioned on these forums regarding high idle that was not on my list was the O2 sensors. Could the failed rochester failed cause damage to the O2 sensors?

Any ideas a greatly appreciated.

 

Does "Reset ECU" mean they did a TPS calibration using the software?

 

When the TPS was replaced (which was the last thing done to the car) I believe it was also calibrated.

 

I would make sure. After two years of fighting mine, that is what fixed it. The ecu will not attempt to control idle unless it sees the throttle at ,well, the idle position. So if there is any miscalibration, it will not do the control.

 

This sounds like the exact problem I was having with my idle when my IACV was plugged in after trying the ECU out in a regular XJ6 (stupid, I know. But I like to experiment). I ignored the problem for about a year by just unplugging the IACV and constant idlle (cold start or warm) was at a constant 800/900rpm.

Just a few months ago I finally got ahold of a replacement ecu and tried it with a the IACV plugged in and it controlled the idle fine. It just needed the o2 sensor orientation and TPS calibration (sparkenzap's advice) and now my idle is fine.

When I was calling shops around locally to see if they could do the o2 sensor orientation and tps calibration, most thought I was talking about an ecu reflash and I thought it was the same thing. They tried to reflash my ecu I guess but couldn't get it to communicate correctly and then I realized I had to tell them specifically to do the calibration and orientation and within 10 minutes it was done.
I would recommend telling the shop to specifically do the orientation and calibration. They could've been trying to do something else all along...

 

us the need to Joeguar, check your EGR valve, there is an official recall on that part, it is the part that causes high RPM, plus the change of e prom

 

I had a 1995 XJR and over the course of the years battled a high idle problem a three times. A couple times it was relatively easily solved by throttle body cleaning. The third time, though, throttle body cleaning didn't help and I was preparing to delve into electronic controls, something I wasn't looking forward to. By this time in my relationship with the car I referred to is as "The Tormenter" and thought of myself as the enabler who, for some dark and deep-rooted reason, likely related to lack of self-esteem, felt that my normal role in the relationship was to play the victim.

Anyhow.....

For some (now long forgotten) reason I decided to slacken and then re-adjust the throttle cable. Voilá, persistent high idle problem solved.

There is a Jaguar-specified adjustment procedure. A search should locate it, as it has been posted a few times. It never made much sense to me. I simply slacked the cables and then re-tensioned them until there was just a touch of slack. If the engine speed increases you'll obviously now you've gone too far.....and a very tiny bit 'too far' results in an exaggerated increase in RPM.

At various times I've speculated, but never investigated, the possibility of the traction control unit playing a role in this. In essence it's merely a small motor with a pulley system to push the throttle cables. If the motor was binding or sticking in some way....well, you get the idea.

Just throwing it out there.

Good luck.

Cheers
DD

 

No EGR on the 1995 XJR, at least not the USA market versions.

Not sure where the OP is located.

Cheers
DD

 

I had a similar high idle problem on my 1995 XJR. Turned out the throttle cable "boot" that goes into the traction control unit had broken, so the cable was binding inside the sheath and not allowing it to return to idle. It's the hard plastic piece that holds the throttle cable into the traction control housing on the right side of the engine bay.

The throttle cable is also zip tied to the rear of the engine bay, making some sharp angles. I cut those and routed the cable over the engine to make the bends more gentle and the idle returned to normal.

 

I contacted the mechanic that replaced the TPS and he said that it was calibrated with the Jaguar software. He also said that he analysed the information fed back from the O2 sensors and they appeared to be functioning as they should.

As for slackening and readjusting the throttle cables, that was one of the first things I tried when I decided to start addressing the problem. I had a bit of a look at where the throttle cables attach to the traction control unit and everything seems OK.

 

 

I completely agree with Doug - the throttle cables if not correctly adjusted will result in high idle speed.
I could walk out into my garage right now, tinker with both cable adjustments & bingo, fast idle.
You have to get them correct, both the one from the accelerator to the traction control unit & the one from there to the throttle body.

John Herbert

 

I just removed my fuel rail on my 95 XJR to replace an injector and clean the others and after I re-installed the fuel rail I had a high idle. It was because i moved the throttle cable out of the way and that minor re-routing raised the idle.