The TPS is on the underside of the throttle body. See part number 2 in the diagram at the link below:

Throttle Body Assembly-3.2/4.0 Litre-Normally Aspirated - Parts For XJ Series from (V)720125 to (V)812255 (X300) | Jaguar Classic Parts UK

Regarding the IACV, you can clean the black gunk on the valve and the port in the TB with carb cleaner and a small brass-bristle brush. If you drive the car with the IACV disconnected and idling at 1000rpm, you may have rough gear shifts that could potentially cause transmission damage, so that would be one thing to be aware of. Others may have other cautions to add.

Cheers,

Don

Good catch, Ross! Which presumably could also be caused by a gunked-up throttle butterfly valve that can't physically close to a proper 0.002 in. gap, so the TPS would not provide the idle position voltage to the ECM...?

Yes, that is certainly possible, and I might guess it is the probable error mode for the gummed throttle plate, since the IACV is supposed to regulate the throttle in spite of minor disturbances in the closed throttle air gap.
I would caution Stu about changing the TPS without a good diagnosis- it is relatively expensive, and the "official" setup procedure for a new one uses dealer level software to run a TPS calibration. Some have been lucky and reported that the new TPS worked with the old calibration and others have elongated the mounting holes to do a mechanical calibration offset, but I think a good dose of luck has been on their side.

I would first check the ecm relay behind the passenger side headlight. there is also another relay in the fuse box under the hood and I believe this is the relay for the crank position sensor but memory is a little fuzzy right now. Very easy fix, very cheap fix and is common with the symptoms your car is having. I would tell you that you have a bad coil, but you do not say that the dash lights go all crazy on you when you stall, another common symptom.

So many replies. Thank you !
I think this is now going to have to wait until my next set of rest days. Doing 5 on then 4 days off. The oc vis going to stay unplugged until then but I've not had any rough changing in the auto box and no lights on the dash.

I've plugged it back in now as it smelt rich

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Can anyone recommend a link to buy the idv please. Thanks

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Hi Scorpio stu,

I'm not sure which part you mean by "idv." Are you referring to the idle air stepper motor, the idle air control valve or manifold, or something else? How have you determined that the "idv" needs to be replaced?

Don

See Don that's what happens when your on a night shift tired lol. I was talking about the idle control valve. The icv !!

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Stu:'The ISSC is fairly expensive for these engines. Help remind me why you think it might be bad?

Is iscc the same as the idle control valve as I think that's what the problem is. If I unplug it the car doesn't stall and runs lovely. If it's plugged back in the car drives ok but will inevitably stall when slowing or stopping

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Well, I would say that the ISSC itself is almost certainly fine- It is moving. Now, why it controls to a position that stalls is another matter. In my case, it was the TPS and then miscalibration of the new TPS.

Ross,

The stepper motor from Jag is quite expensive but I found that the exact same motor, mount and all is used in a Renault Megane from the late 90's and those units are cheap as chips

Allan:
Thanks! Thats good to know, but in Stu's case, the fact that plugging the motor in makes a difference means it is moving some. Of course, it could be all gummed up and missing steps, but the control action is to close the stepper after power down, then the number of steps top the last controlled position on startup, then control when the TPS says you are at idle, plus some other conditions.

By teh way, where do you find Renault parts?

Ross,

Totally agree with you, I was just commenting on the cost for a Clio/Megane version of the stepper. I got mine from England but I'm sure anywhere in Europe would sell them. Shipping is cheap as it small and light. I don't have the part number handy but will post it here when I dig it up. I think I paid less than $25 delivered.

Boy, I wish I knew that before, when I launched the pintle out of my ISSC, while trying to clean it! I think I pain nearly $300.00 for the new one? I found th epintle when cleaning up the garage a few years later, but I had already thrown the body away.

I found my Megane stepper motor via an eBay seller from Germany - same price range as Allan's. The stepper motor is the same part for the 4.0L/3.2L XJ40s and the X300s, and as Alex Koch, one of the Jag-Lovers XJ40 forum members discovered, the Renault Clio/Megane part is an exact replacement. Here's a link to photos showing the part I bought, made by the German company LÖWE. The label on the box was damaged, but according to the eBay listing, the LÖWE part number is 57174, EAN Code 4260278050633; Reference / OEM: Renault D95174, D5174, B335:

Welcome to Jag-lovers - Members Photo Viewing Page

Cheers,

Don

My 1996 XJ6 has begun doing a similar thing. The engine just dies for about 1 second and then recovers. I've observed that during the outages the battery light on the instrument panel comes on, however it's not a complete electrical outage, as the radio is not interrupted. I'm thinking that it's an electrical, rather than fuel, problem, as it does not seem that anything but electrical could fail and recover that quickly. I'm going to begin looking at the schematics to see if there's a relay in a position that might account for this.

I am extremely lucky that I found out what problems faulty ignition coil packs will cause before I spent money on other things like fuel filters and pumps,CPS,ECU issues,TPS and transmission diagnosis. I simply replaced the coil packs in my Jag and she has been purring along ever since.
Before I replaced my bad coil packs my car was acting absolutely crazy. Idling high,low shutting off at any given moment,dash lights flashing like a Christmas tree, transmission limp mode light coming and going. Even the airbag indicator would illuminate.
The new coils solved all those issues. My car has been running perfect for 23,000 miles. If it acts up again I'm going to just replace all the coils before I do anything else.
I replaced all of mine with 2000-2006 Lincoln LS V8 coils for $8.50 each. They have proved reliable enough for me. So far 23,000 miles.
I would hate for you to spend the time and money chasing all the those other symptoms when you only have bad coil packs.

I read a lot of posts about stalling, as my Vanden Plas was stalling at completely random times even though it was idling well. I'll be damned, I put in a set of ordinary Autolite plugs, carefully gapped, and no more stalling! The old plugs didn't look bad but I think the computer was actually shutting off the engine due to the plugs. One great, big thank you to you for your post! Cost of fixing annoying and dangerous problem: about $13. Thank you!