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Matt
Matt, Mechanical Engineer
Category: Jaguar
Satisfied Customers: 21616
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 96 X300 XJR with an idle speed problem Have removed

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I have a 96 X300 XJR with an idle speed problem
Have removed and cleaned the air intake
Replaced and correctly calibrated the TPS
Replaced the Idle Speed Control Valve with known good one
When warm the engine starts and settles to 900rpm for a few seconds then ISCV clicks and up she goes to 1100rpm
After reading previous answers I removed the ISCV plug after 5 seconds of running turned car off waited 15 seconds and repeated etc this got the car behaving exactly as it should, it would start, settle at 500rpm ISCV would click and then up to 700rpm.Perfect!
Started and stopped 10 times in quick succession and every time it idled perfectly at 700rpm
Had a cup of tea started up again and back to where we started at 1100rpm.
Where do I go from here?
Incidentally the radiator cooling fans always come on with the ignition regardless of whether the engine is hot or cold.
Submitted: 1 year ago.
Category: Jaguar
Expert:  Matt replied 1 year ago.
Hello This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Customer: replied 1 year ago.
If you re-read my question you will see this is not the problem, the engine does not run rough, there is no hissing and all plumbing is in good order, the problem is the speed at idle, air can only get in through the ISCV when the flap is closed so this must be the problem, indeed I can calibrate it as described but it doesn't seem to keep the setting for more than a few seconds before returning back to running fast.
I think this is electrical rather than mechanical?
Expert:  Matt replied 1 year ago.
hello thats possible however if you disconnect the ISCV then the engine should idle at about 600rpm when warm, if it doesn't then increase the throttle butterfly opening on the set screw to achieve this then see where you areif its still very erratic then yes I'd consider replacing the valve
Customer: replied 1 year ago.
Okay, assuming I replace the ISCV valve how do I calibrate it?
Customer: replied 1 year ago.
From what I have read it is a stepper motor
It has 4 wires going to it
Expert:  Matt replied 1 year ago.
hello calibrate is as followsRun 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 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.
Customer: replied 1 year ago.
Just done a calibration and got the idle speed correct but once again after 30 mins or so it "forgets" its new setting and goes back to 1200ish.
How does the ECU memory work?
Can I reset it?
Customer: replied 1 year ago.
The car also occasionally suffers with a random completely flat battery after being left for a few days, but not always. Could that be linked?
Expert:  Matt replied 1 year ago.
hello the ECU memory is a ROM type CPU so when the settings are written in they should stay coded in providing battery power isn't lost as this resets all the settings to the factory default so yes the random flat batteryness could be the issue hereNext I'd check the current drain aspect, the best way to find what circuit is causing the excessive currant drain is to fit a current sensing multimeter in series with the positive battery lead on the car and the battery, or use a current clamp meter on the battery positive cable. A typical current drain with everything off and un-alarmed should be around 0.05Amp and if its higher than this remove a fuse and re-measure, if measurement doesn't change then replace the fuse and remove the next. Once you've isolated the circuit with the excessive drain check the wiring connections and plugs to components and the wiring harness that runs by the engine bay fuse box - the wiring harness chaffs / rubs through and gets damaged - but its not always easy to see so be careful when checking.. Also check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright. if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement And one last thing is – how old is the battery? – As even good quality ones need replacing every 5 years and faulty battery just won’t hold a charge
Expert:  Matt replied 1 year ago.
Hido you still need help?Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you
Customer: replied 1 year ago.
Have not forgotten but problem is still not resolved
I am taking the car to an auto electrician today for his opinion and will let you know the result of his findings.
Regards
Expert:  Matt replied 1 year ago.
understoodjust get back to me on this postgood luck
Expert:  Matt replied 1 year ago.
Hido you still need help?Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you
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