Hi,


I've been experiencing a high idle condition on my '96 4.0l Celebration for the last two years. Car has covered 38,000 miles.


The engine does smell very rich at startup.


I took it to my local "Jaguar Dealer" and they reset the idle to 800rpm and it was fine for about 4 months and the problem returned.


There are unfortunately are no Jaguar dealers or specialists on Guernsey, the above garage service/repair about a dozen other different makes so they are probably not the best choice; but I have no other alternative.


They also hate the XJS because they can't plug a laptop into it and it will magically tell them what's wrong, so most of the time I have to figure these problems out for myself. They quoted me £700 to fix a lighting problem and all that was wrong was a faulty £5 relay.


The car has had a new throttle body, and an idle controller. The TPS I've left alone as I think that's ok.


One thing I'm wondering about is water temps. The temp gauge only ever gets up to just past 1/3rd on the gauge so could the temp sender be misleading the ecu into over fueling? I always assumed that it should read halfway once the engine was warm?


I have a new thermostat which I haven't had chance to fit yet but as the temp sensors are only about £11 I would be willing to give it a shot if any of you think it may work. I see on the 4.0l there are two water temp related sensors.


EDIT: Ok, I see that one sensor is easy enough to get hold of, the other less so easy....


Anyway to recap:


1. Engine starts and runs 100% fine.
2. Engine idles at 1600 at cold and drops to 1200 one the engine is warm.
3. If you put the car into neutral when it's rolling it causes the RPM's to skyrocket to 2500-3500rpm, this then settles back down to 1200 once the car has stopped.


I would like to get this sorted as it puts a lot of strain on the transmission (when going from park to drive for example).


I've got the car booked in for Thursday so I assume the issue will resolved again albeit only temporarily.


Thanks everyone.

 

"I took it to my local "Jaguar Dealer" and they reset the idle to 800rpm"

What did they do to reset the idle?

 

There's a pretty simple procedure to set the idle yourself, below.

I was able to do it pretty easily on mine after I replaced the IAC Valve.

If you can find the IAC Valve (top of motor, behind throttle body/air intake, called "stepper" below), then just remove the connector as indicated.

I did not have to mess with the "air bypass adjuster", but I think it's just a matter of using a screwdriver.

Padre

From: AJ6 FAULT CODES AND IDLE SETTING / AJ6 Engineering

3.2 & 4.0 Litre

Run engine until fully warm.
Switch off ignition.
After 5 seconds switch on ignition - wait 5 seconds - remove connector from stepper motor.
Switch off ignition.
Wait 15 seconds then replace connector on stepper motor.
Repeat operation sequence 3 - 5 twice - on the last occasion do not reconnect stepper motor.
Start engine and set base idle to 550 - 600 r.p.m. via air bypass adjuster.
Switch ignition off and reconnect idle stepper motor.
Restart engine - idle speed should now stabilise around speed shown below.
Check idle CO as for 3.6 (if non-cat).

Specified Idle Speed.
Cold in neutral - 800 (Auto)
Hot in neutral - 700 (Auto)
Cold in drive - 650 (Auto)
Hot in drive - 580 (Auto) (3.2L = 650)
Hot in Neutral - 800 (Manual)

Note: Cold idle speeds will be slightly higher at very low temperatures.

If the above procedures do not result in stable idling check that the throttle potentiometer is correctly set. Whilst the ECU will automatically compensate for minor errors within the range of the adaptive memory, a badly adjusted throttle potentiometer can cause spurious drivability and idling problems.

Correct potentiometer settings at closed throttle are:-
3.6 = 0.32 volts.
3.2 & 4.0 = 0.6 volts.

 

That procedure didn't fix my 1996 car either.

You need to find a shop with a PDU (best choice) or WDS. They seem to be able to do it. You will not be able to fix this yourself.

I've gone through this already. By replacing the throttle body you have eliminated the usual suspect which is a sticking throttle body butterfly. Perhaps the TPS can be bad too.

Once you get past the throttle body, the next option is to get it reset using a Jaguar computer. Idle should have been reset to about 600 rpm, by the way.

I hate to rain on your parade, but I've been there and done that. You can go through my old posts and see all of the misery I've been through with high idle.

Now, if you haven't had anyone check for vacuum leaks, that could be another suspect.

 

Hello matey.

I'm actually not sure, being that they have to service a dozen different makes I doubt that they would have the original jaguar service equipment but I will ask next time out of curiosity. I was just glad at the time that it was fine again.

 

Thanks mate. Yep my bad, it was some time ago that it was reset but it must of been 600rpm.

My gut feeling is that it's something stupid. Usually is.

As I say though my local dealer dooesn't like the car much because of its age.

There is one thing against me. Guernsey being a small island means one thing. Lots of short journeys.

The issue though started just after I'd been to Europe. I noticed the idle gently bobbing up and down. 600 to 700rpm.

I did clean the throttle body a little while back. Some black residue in there but nothing major.

I did try the fix mentioned above and it did work albeit only briefly. After about a minute the engine starting high idling again. Thanks for the post though. No harm in trying again.

Thanks for the help though guys.

 

True for an AJ6 but he has a 1996 with an AJ16.
No air bypass adjuster.
Full reset requires a PDU.

 

I don't know about the XJS, but on the saloons with the same engine there is an adjuster in the throttle cable. The 96 should be OBDII compliant, so if you buy a reader that shows the data stream you can see what the computer thinks the throttle position is at. Normal idle is about 12% throttle or so.

If the throttle is being held open further (or the TPS isn't giving the proper reading to indicate idle) then the computer sees that the throttle isn't closed, and will make no attempt to adjust the idle air valve.

As a quick and dirty test, I would disconnect the throttle cable from the throttle body and see if it idles at the proper speed. If so, then you know it's in the cable. If not, then look at the set screw that determines where the throttle stops at idle, and adjust to make it close tighter.

 

The base position of the idle air valve can only be set using a diagnostic computer, the procedure posted above is for the previous generation engine and management system.

All that being said, if you're willing to invest some time and energy there is a way to replicate the Jaguar diagnostic tools. You need an XP laptop and a cable (mongoose cable) that can communicate with the OBDII port. Software was available to download here, or I've seen it on Ebay. The cable is the expensive part, Don't get the Chinese knockoffs, buy the genuine from Drew Technologies. About $600 USD. There is a massive thread on the forums here about it: https://www.jaguarforums.com/forum/g...an-tool-66558/

 

One other thing I thought of: The AJ16 is fairly notorious for having sticking throttles. The throttle shaft is vertical, so any oil vapours and gunk coming in from the crankcase ventilation system will gum up the throttle shaft and cause it to stick. Fairly common on cars used for short trips where things don't get fully hot.

However, you said you had the throttle body replaced, so that should eliminate it as a cause. I assume it was a new part they used?

Can you turn the throttle by hand to close it and see if that helps? Maybe try opening it fully (ignition off) and snapping it shut? I had a saloon that wouldn't return to idle unless I gave a very vigorous blip of the throttle to cause it to snap shut. Gently easing off the throttle would cause it to not close fully.

If it's a sticky cable, those are still available from Jaguar. Part number MHD4620AC (I assume you have a RHD car?).
Accelerator Cable-Rhd - Parts For XJS from (V)179737 to (V)226645 | Jaguar Classic Parts UK

Looks like that doesn't have the inline adjuster I was thinking of, but there is an adjustment by the nuts that hold it to the engine.

 

Save your money. I have that. It will (1) reorient your oxygen sensors (2) reset your throttle potentiometer. It will not reset idle adaptations.

I saw some posts stating that the Genrad 510 will do it, but I've asked users and it doesn't appear to do anything the Mongoose does.

Find a service station with a PDU or WDS.

 

Thanks very much for all the help and advice it's all useful information.


When the issue occurred previously, I cleaned out the throttle body the best I could (I see Vee recommends taking it completely off the car in another forum post on this subject matter).


It initially made no difference but when I pushed on the butterfly valve there was a tiny amount of movement and that sorted it. It wasn't down to 600rpm but it was close enough.


On this occasion though, no matter how much cleaning I do it doesn't make any difference which is disappointing. The throttle body is spotless.


The adjustment issues are not totally applicable on my version of the car.


The throttle body mechanism is on it's farthest travel, there is one adjuster screw but that would make the idle higher.


Yep, the throttle body was a new item when it was fitted. I also fitted a new Idle Control Valve (the piston on the top side of the throttle body, sorry it was a little while ago now so apologies if I've named it wrong).


Being a UK car it doesn't have all the emissions equipment the US cars do, which I see causes the odd problem!


It's been a little while since I've looked into this issue so posts by Vee and some of the others on here simply point to a reoccurring issue with this model of engine.


As you say it may simply be a case of Jaguar resetting the idle map on the service equipment, and then maybe cleaning the throttle body every three to six months or so.

 

I've actually taken things a step further regarding keeping the throttle body clean.

I've disconnected the hose from the cam cover so that it no longer feeds oily air back into the intake. I have been meaning to install an oil catch can, but for now I blocked the intake hole at the elbow and I've simply run a hose down from the cam cover so that it exhausts below the engine. Not a permanent solution, but I'm getting there. (I also blocked the hose from the oil pan that was to collect oil from the pitiful separator Jaguar added later on.

This should prevent any more grime from gathering at the throttle body.

I think you need the PDU to solve your idle issue. I believe the WDS can do it too.

 

Hi everyone.


Quick update for you all.


The Jaguar dealer is unable to sort the problem.


The diagnostic equipment is showing no problems so the mechanics suggestion is that the car needs a new TPS as that may be contaminated.


This could be correct because as I mentioned earlier, the idle started to slightly misbehave after a 2,000 mile drive across Europe. So maybe all the mileage has fouled up the sensor.


I would much rather do the work myself so I'm getting the car back, will fit a new TPS and thoroughly clean the throttle body again.


I assume the dealer will still need to reset the idle using the diagnostic equipment but I don't want to spend £400 labour on a sensor change when I can do it myself.


In typical Jaguar dealer fashion they've advised me to change the front discs, pads and rear pads at a cost of £1000. No thanks, they're fine. I know...I changed them last year...lol

 

You can try that, but that's what I was told by a dealer when I first got the car. They wanted $2,300 for a new throttle body and an additional $700 to replace the TPS which they said "usually breaks when they try to remove it".

Pure BS.

The throttle body was fine, I needed to get my fuel adaptations reset. Stay away from the dealer, they are not your friend. I doubt that there's anything wrong with your throttle body. I suppose you can buy one on eBay and install it yourself.

If you're not getting any kind of sticky feeling at your gas pedal, it probably isn't a gunk issue.

It cost me $150 for a shop to fix my problem with the proper equipment. I think you really ought to take that car to the mainland and find someone who is capable of fixing it to fix it.

Maybe contact Harrison Automotive? They seem to advertise experience dealing with older cars, including Jags, and are on the island!

 

Hi Vee,


Yeah I know. it's a bit of a problem to say the least.


The dealer is the only company on the island with the Jaguar Diagnostic unit that can rest the idle parameters.


Having said that though, they only charged me for the A/C top up and that was it (and they knocked 20% off that as a good will gesture so I can't complain too much).


Harrison are great and they did a great job of repairing the key marks on my Dad's Daimler but I'm afraid they are a restoration, paint style company. I think all the engine, mechanical work they outsource to UK companies.


They don't really have the equipment to deal with the problem I've got which is a shame.


It costs about £300 to get the car to the mainland, so I'll try a new TPS (as it's about half that) and see if it works.


If it doesn't then I'll start saving to get the car to a specialist to the UK, there are a few very good ones in the south of England.


It's not a major problem just an inconvenience at the moment. I'm just working my way through the nagging list for the car before I start on getting the bodywork sorted. Which will probably be with Harrison Automotive


I'll keep you all posted though as thing progress, always helpful to others.

 

Andrew,
Did you ever get this fixed? I have some on the same issues.

 

Hello my friend.


Well yes and no...


As I've mentioned above I don't have a Jaguar specialist on Guernsey to rely on which makes my situation slightly more difficult than others.


Ideally I need to find a specialist with the Jaguar diagnostic unit to reset the idle parameters on the throttle and until I do I'll have to live with the problem.


However I have two updates for all of you on here.


When I received the work report/invoice from the Jaguar dealer on the island I was not best pleased. It stated that they tried to plug in the diagnostic kit but it was "incompatible" with my car and therefore they ran no diagnostic work on the car (even though they charged me £100 for it). The mechanics suggestion was to replace the throttle body, stepper motor and the throttle position sensor and the redo the diagnostic again (which is pointless if they don't have the correct diagnostic machine in the workshop).


However rather than have the garage throw tonnes of my money at the problem I did purchase a new throttle position sensor because the original was 20 years old and dirt or muck may have got inside so it was worth a try.


Last week I removed the throttle body and upon closer inspection I noticed that the Jaguar mechanic, rather than remove the throttle body to inspect the stepper motor (the bolts won't come off without removing it) he'd tried hacksawing them off instead as there was marks in the tops of the bolts where he'd tried to cut groves. I assume to try and see if they were tight.


There was also a few bolts missing where they hadn't put everything back so I sorted that as well.


Took the throttle body off, removed all the sensors and thoroughly cleaned everything with throttle body cleaner, fairly mucky but not too bad.


Re-attached everything with the new throttle position sensor, ever so slightly adjusted the grub screw on the throttle body as I noticed the throttle was a tiny bit out (and I do mean tiny, less than a mm).


Started the engine but unfortunately there was no real change. Idle still fairly high at 1400rpm when the engine is cold.


Oddly the car will sometimes drop to 750-800rpm when warm which it never did before so the new throttle position sensor has had some positive effect but it's not quite perfect.


So In the last two years I've replaced the throttle body, the stepper motor and now the TPS.


The issues started to surface when I took the car across Europe a few years ago, I noticed the idle was bouncing ever so slightly when I got home and it got worse from there.


It's a shame you can't hire out the correct diagnostic unit for this car, I wouldn't even mind spending some money on a second hand one as it would pay itself back pretty quickly when compared to the hourly rates the specialists charge. Also my Dad has a XJ12 which requires exactly the same unit so it would come in useful.

 

There is a VCM for sale on this forum...

That may perform all the tasks you need.

 

Vee,

A VCM? I thought a PDU or WDS was the programing / calibration tool that we needed.

Has anybody taken their car to Authorized Imported Car in Flemington NJ?