It was all too good to be true. Air con fixed earlier in the summer and working beautifully. O2 sensors replaced and car returning 24 mpg on gentle runs (an XJR !!!). Idle speed perfect at 650rpm when warm after a new TPS a couple of years ago. Everything working, and just passed the 170000 mile mark.
Happy days, until today.
I started the car as usual, and she caught straight away on all cylinders, but just ran the rpm down and stalled. Repeated several times, exactly the same. I can catch her with the throttle pedal, and she runs fine, and drives fine.
i scanned for codes, but there are none. I checked the live data and both the IAT and ECT seem plausible. She goes into closed loop normally, and comes up to temperature normally.
I managed to persuade myself that the battery could be low, but charging it up made no difference.
It is as if she has lost idle.

Any ideas guys?

Thank you in anticipation.

 

I'd be checking the idle air control valve, intake manifold, crankshaft position sensor, loose cables and hoses.
Then take a look at the fuel pressure, pump, filter, etc.
Mine is NA, so maybe there's more to check on the supercharger.
Any luck starting it since?

 

She starts perfectly, just won’t idle. I’m thinking IACV has died but trying to think of alternatives first as it is such a pain to get to it on the supercharged cars.
MAF has crossed my mind, but not convinced.
does anyone know how to test the IACV without removing it?

 

Just a thought,

Both mine, the 3.2 and the R.

Like yours ran sweet as with the boot on the pedal.

The 3.2 was sadly "gooed" throttle body innards.Cleaned it out YUK, good as gold.

The R was the same, and cleaning that helped, but IACV was the mongrel at play, and I simply handballed that to the Indy down the road. Walked back to the pub, between my house and the Indy, and waited. 4 hours later, done. Lunch was awesome, and I still had clean hands, winner.

 

Thanks for that Grant. When I had it apart to replace the TPS, there was remarkably little gunk, and while I didn’t know when it was previously apart, I know it had covered at least 50000 miles in my latest ownership so I would be surprised if it was gunked up now. I have ordered a new IACV as I think it must have died, given how suddenly idle went from perfect to dud. I have a spare MAF which I will try as it is an easy swap, but have Sunday pencilled in for yet another deep dive on the throttle body.

 

The IACV can be checked to see if it's working:

1. Run engine until you reach normal operating temperature.
2. Switch ignition off.
3. Switch ignition on, wait 5 seconds, then disconnect the connector to the idle speed controller.
4. Switch ignition off.
5. Wait 15 seconds then reconnect idle speed controller.
6. Repeat two more times.
7. On last repeat, do not reconnect idle speed controller.
8. Start the engine.

Check the base idle speed, which should be at 550-600rpm.

Switch ignition off and reconnect the idle speed controller. The idle will likely be back to where it was before.

Let me know what happens.

 

Vee,
Many thanks for taking the trouble to set out those instructions, which I guess could serve to "re-index" / re-learn the stepper motor.
The problem I have is that on the supercharged car, the IACV cannot be accessed without removing the elbows into and out of the intercooler, which takes the MAF out of the loop. Also, even with them removed, I can barely reach the connector, and having managed to get it off, it takes considerable time and dexterity to put it on again. I would not be able to meet the timings you set out. On the normally aspirated car, it would be very straightforward as the IACV is in plain view.
I cant access the two small bolts holding the IACV on, so I am resigned to removing the throttle body. Fortunately I have a lift, and am going to try from below, avoiding disturbing the inlet manifold, but still an imperial PITA!

 

When you have your throttle body out and off for your operations, Turn the IACV 180 degrees the other way and yes the cable connecter is very bearable to reach without all the theatrics. Make sure the throttle arm clears this connecter on reinstall.

Thank you.

Larry Louton

 

I usually use a butane 'pencil-torch' to loosen the thread locking compound on the IACV fasteners.(and TPS fasteners)

I gathered up the one's that had broken bolts from the dealer shop floor after the other mechanics got in a hurry and snapped them off.

They would just tell the customer that the throttle was faulty and get another from the parts dept.(very expensive new)

A little heat and some drilling/slotting on the broken bolts, I had good-used throttle assys that I sold on eBay for a few hundred dollars each.

You might need a TPS and Oxygen Orientation setup when you get done? (I do both at the same time when I connect WDS/IDS)

 

i killed 2 of the $5 ICVs, they suck and fail exactly the way you’d expect them to. if it’s an XJR you should probably get the real one.


if you can get it to work for a while, leave the car on at warm idle ac on and then unplug it. i’ve been driving around like that for months

 

Guys, thanks for the input. Some progress to report.
After my last post, I went to put the car on my lift pending the arrival of the new IACV I had ordered. Since she had last run, I had managed to disconnect the IACV once in situ, attempting to follow VEEs suggested procedure. To my surprise, she started and idled without my assistance on the accelerator.Switched her off, she started but wouldnt idle. Odd
Managed to undo the throttle body from below, and move it without undoing the coolant hoses or the throttle cable, which enabled access to the IACV fasteners. These came out without a problem, as I had eased them out when I had last had the throttle body off a couple of years ago. Old IACV and the throttle body spotless. Fitted new IACV (180 degrees out, thanks Larry) and reassembled. Much less hassle than I had feared.
Started her up, and she idled, if slightly erratically at first as the IACV seemed to be indexing itself. Declared victory, and retreated indoors for refreshment.
Next morning, back to square one, she wouldnt idle. Took her for a drive, and a degree of idle control returned, but was lost on shutdown. Resolved to fish out my IDS / mongoose combo and look to see if there was a calibration option.
I have never had much joy communicating with the car this way, and this time was no different. I couldnt persuade the mongoose to connect, although in my attempts to do so, the ignition was left turned on for quite a long time. Guess what, she started and idled perfectly!
Never one to look a gift horse in the mouth, I have concluded that all is now well, and that the prolonged ignition on time allowed the IACV to calibrate. Time will tell. Peace in our time!
Thank you all again for your help

 

The procedure I gave you is only a test to see if the IACV works. After restarting your car, it usually goes back to doing whatever it was doing before…basically, I believe you only proved that the IACV is indeed working?

Keep us posted on progress.

 

Vee,
She now seems to be functioning completely normally, so as I write, all is well. I am not entirely clear as to the explanation for the chain of events which I have encountered, but applying Occams razor would suggest that the old IACV died, and I had to leave the ignition on for a few minutes to calibrate the new one. Intuitively though, I think there is more to it.
I now doubt whether the old IACV was broken at all, and suspect that some form of electrical "event" caused the loss of the IACV calibration. Leaving the ignition on may well have sorted the problem without doing anything else. I am holding on to the old IACV as a spare at this point, and will see what the coming weeks bring. History would suggest that if there is an underlying issue, it will manifest itself soon enough....

 

Error

 

The IAC is a 4 wire stepper motor and you can check the legs ( winding ) at the ECU black color connector

There are 9 test lead positions

R - G

R - N

R - U

Then

G - N

G - U

You have already checked G - R as R - G

and so on

You may not see a fault until the step motor heats up and mechanically banging on the step motor side so a old school needle meter is preferred

The EGR ( if your car is equipped , with the 2 solid lines , one going into the aft bank exhaust manifold and the other going into the forward bank ) does have a follow-up position sensor that you can read with a meter

There is a PID label EGR_error that can be seen with a ELM327 reader and I wouldn't expect it to be a perfect 0 %

There is also a separate EGR temp sensor other then the IAT sensor on the inlet elbow I think on the # 3 intake manifold pipe but again it would be buried under your supercharger package

See page 62 "Control Module Pin out Information " Red colored ECU connector Papa Indy 104 pin 3

The voltage on that wire should be 4.9 volts DC at idle which will be a closed EGR valve

jagxj1996.pdf (jagrepair.com)

The EGR position sensor should read 0.7 volts DC at idle ( closed ) on the Red ECU connector Papa Indy 105 pin 15

The Evap valve should be X at idle and can be tested for clicking with a 9 volt battery

See again page 62 Red ECU connector Papa Indy 104 pin 34

The question if it should be open or closed on idle and my understanding it should be closed , Therefor you can cap off the line from the bottem of the intake manifold to the EVAP volve for a test configuration ( a manifold possible source of vacuum leak at idle ) .... corroded , leaking vapor condensation stainless steel canister in the back and it's relationship with the Rochester valve in the back ) not all X300s use this Rochester valve

See page 60 of the AJ16 Engine Management Systems PDF

www.jagrepair.com/images/Training Guides/801S - 2000.pdf

 

Hi All This thread caught my interest because it's current.I'm trying to save my 97 VP.I've yet to find this stalling issue resolved in the forums

After 30 min. drive it stalls on decel. / stop. This leads me to believe it's iacv which seems to be fine up to the point of stalling.
I've had car for 7 yrs 68,000 - 110,000 mi .This year I had 1 severe coil misfire ended up replacing all 6 with uro coils with brass ferrules and white potting, new champion plugs,new ckps and rebuilt mafs chasing down start/ stall issues.all obdII data appears to be nominal and it starts fine runs well from cold

I'm hoping those involved in this thread could shed light on my issue.

 

yes that’s how it failed on mine

pull the iacv at warm idle and see if it still stalls

 

more info please
if yes then what?
if no then what?

 

if car idles fine you can drive it around with no iacv for as long as you want or replace it

if not something else is causing the car to stall

 

I have a vague, indeed very vague recollection of an issue whereby low transmission fluid can cause a stall on deceleration. I have not encountered it myself, and it is a vague recollection, but I guess there isnt any harm in checking the fluid level?