Hi - on my XJR 4.0 sc 2001 all of a sudden on start up this morning she went to 1700 revs then only down to 900 on full temperature rather then 650 normally. I had previously done 300 mile trip without issue.
I sensed something was wrong then I pulled over and engine failsafe mode came on.

about a month ago the same thing happened and I replaced the MAF, cleaned the butterfly and she was cured.
I stopped off at my local garage and the owner diagnosed it with the snap on code reader as P0706 idle speed too high… but that doesn’t really tell us much. Despite him resetting the codes, doing hard reset it still won’t clear….
The TPS was replaced only 8000 miles ago.
He said there could be a vacuum leak somewhere but would need to go in…

can anyone confirm there’s also an idle speed control valve on these and tell me where it’s located? Can they be taken off easily and cleaned? I’ve done this on my Fords and that seemed to clear those issues. Or is a new one recommended?

can the lambda / oxygen sensor throw these codes?

I also see “engine coolant level low” intermittently, but on checking it seemed fine… which is weird.

other than that I’m at a loss as to what I can do!
cheers !

 

Sounds like the tps needs to be readjusted to me. I’ve experienced a couple of those when replacing the tps before. Maybe one of the screws may have not been tightened enough and vibration over time kicked it out of adjustment??

 

There is no separate idle speed valve. It is all done by the main butterfly. TPS voltage could be out of area. But it can be too that tps and therefore butterfly are in correct position but engine speed is too high due air leak. Lambda sensors can't make engine to rev up.
Idle speed high code means that ecu couldn't drop the idle speed down to the target speed due fault outside of it's known area. So it does not know what the reason is and won't give straight to the point code of it.

If coolant level is correct and level sensing is acting up, then it is the sender in the expanstion tank that is sticking.

 

P0706 is a transmission (W5A-580) code, means problem with the gear selector switch. May need cleaning or only adjustment.

 

It does sound like either the TPS or more likely the unmetered air leak, a rather large one sucking air in - a simple smoke test around the induction, or carefully spray carb/brake cleaner around the induction path - if the revs rise in a particular spot you're ID'd your leak. The metal gasket under the throttle body and the large rubber seal that connects the throttle to the induction tube are the most likely culprits. Having had the TB off previously, did you replace either of these seals because Jaguar recommend fresh ones to keep things like this from happening.

TPS - like A2B has suggested a slight and I mean tiny movement of the TPS body will take the ECU out of range - and a code posted. Revs will rise in relation to the TPS movement and it might need readjustment.
My money is on an air leak, but having a recent TPS can confuse the issue.

O2 faults are specific to the sensors generally, but can do funny things before going bad, they will post their own codes at that point. A less likely path this one.

There are no speed control valves on this car - the throttle body is drive-by-wire where the pedal cable moves a spring loaded throttle pedal position sensor (TPPS) which tells the throttle position sensor (TPS) where to put the throttle plate with TB's in built motor.

 

Hi thanks ever so much you guys.
P0506 I may have gotten wrong as that’s idle speed too low…it may well have been P0507 which is what I had previously about 4 weeks ago.
when I had that I did adjust the TPS a tiny bit anti clockwise and then after cleaning the butterfly she was fine.
When I adjusted the TPS I couldn’t get the bottom screw undone and could only get the top one off and forced it slightly then tightened the top one back. These screws had a star shape insert and I had real trouble finding the right star head . I just couldn’t budge the bottom one. I think it’s been rounded off.
MSI how do I get it out?

Can anyone tell me what type of screw the TPS is attached with, and, if possible, if there’s a Phillips screw for an alternative?

I hate it that Jaguar tend to use star heads a lot in this model and is annoying.

so I’m guessing from this feedback I didn’t tighten it up enough.. or i maybe need a new sealing grommet for the TB…. Maybe I should order one anyway…does anyone know the part number? I cannot find it anywhere!

cheers !

 

I think they're 'security Torx' T27 or smaller, torx bits with the hole in the centre. I'd have to check. Being a steel bolt in alloy I'd be inclined to whip it off and get a machine shop to centre drill it out, chase the thread, and get yourself some stainless Allen head button/cap heads. Or some sort of TPS sensor protected Dremel work on the head until it clears the sensor hole to remove it. Mole grip the strump out. It's always good practice to mark off the sweet spot in a line from tps to throttle body before removal or for work later on, avoiding the perilous job of finding the low idle once again.

 

This TB is off of my 2002, 50k mile XJR engine that’s never been adjusted. If you look closely, you can see that the TPS bolt is actually a 5 point vs a typical 6 point Torx.



The TS20 is the correct size for the TPS bolt head. I don’t know the thread size, pitch or length of the screw.



I was with Sean on the size thinking it was a 27 but, a 25 wouldn’t even fit. The correct size is a TS20. I *think* the “S” in TS20 only means “security”.

This is the link to the 5 point Torx bit set I got. Protool 5-Point Star Tamper-Proof Bit Set-Fits Many German Cars-T10 to T50-Taiwan, Metal https://a.co/d/1yrQoO2

 

In your first post, you said it was P0706. Are you now certain which code it was?

 

Stojanovic- I apologise, I cocked up. Yes it’s P0507 idle speed to high.

addicted2boost - thanks so much for pointing that out… the 5-pointed star I didn’t have, only the 6 pointed… which maybe explains my frustration and swearing.. however I managed to wiggle out the top screw and wiggled the TPS about the anticlockwise as much as I could then tightened it up best I could. Hard reset the ECU by putting neg on pos for 30 seconds.
fired her up, from cold ( freezing point) still 900 and engine failsafe mode then slowly she started to drop revs until operational temperature, then the failsafe mode went away and she now runs at 650 again…
I checked coolant and she’s lost some so I may ask the garage to check out the system.
once I get the set of TS heads I’ll try and mark the TPS with tipex at the screw heads release the bottom screw and retighten.

cheers !