Can someone confirm this is the proper sequence for replacing an Idle Control Valve?

My replacement just arrived and I want make sure I install it properly on my 96 XJS 4.0.

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

Check the base idle speed, which should be at 550-600rpm.
If the idle speed is not within these limits adjust the air
bypass screw
to bring the idle speed within these limits.

Switch ignition off and reconnect the idle speed controller.
Start engine and check to ensure that the idle speed is
between 650-800rpm.

Thanks - Kevin

Kev,

Suggesting to simplify this - disconnect the battery overnight. Change the ICV and connect everything as it should be. Connect the battery and start your engine. Run until working temperature + additional 15minutes on idle.
Check your rpms after that time. If incorrect. Shut down the engine, disconnect ICV and fire up again. Then you can adjust it with your screw if necessary.
Be aware that revs after connecting the battery may go weird ignore that until fully warm. You may have error displayed after that (just for the moment).

Janusz is wrong here. Idle settings are stored in RAM. You can unplug the car for 50 years and it would not make a difference.

What you have posted is for testing the IACV.

To replace the IACV just replace it. Beware the two 5.5mm screws that hold it in. They are loctited in and will snap. Heat them and they can be undone and reused. If you break them, you’ll need some Timeserts or some kind of thread insert.

Ehmm. Guessing got it all wrong Vee. I was always thinking that RAM is memory got erased after power cut.

Also, I was always thinking that OBD equipped cars were using EEPROM on the very beginning (year 96) and later on - PMC memory to store the settings. I was also wrong thinking that Kev’s got car from 1996 so there is no certainty on memory type and the way it functions aa OBD2 was just introduced then.

I was terribly wrong thinking that battery disconnected overnignt (realistically longer than 2h) will force the ECU to flash PMC memory and start standar calibration of all the systems like auto tranny or ignition/fuel…

As I am not AJ16 owner - I trust your judgement. I have seen XJS with tank installed upside-down from factory, with silicone-filling on all the problematic gaps. So, everything is possible when made in Coventry :wink:

Yes, most everything you posted up there is incorrect.

I think the only parts you could be correct on is that last paragraph, but any information you have on how the AJ16 stores data is wrong.

UPDATE: I believe Janusz is partially correct. The settings are indeed stored in EEPROM, but like other types of PROM, EEPROM retains its contents even when the power is turned off. So he’s really still completely wrong.

Well, I don’t think the idle control valve is my problem. I just replaced my one year-old unit with a new replacement unit and went through the sequence below.

  • Switch ignition on, wait 5 seconds, then disconnect the connector to the idle speed controller.*
  • Switch ignition off.*
  • Wait 15 seconds then reconnect idle speed controller.*
  • Repeat two more times (steps 3* - 5)

After completing this sequence three times my idle zeroed in on 850. I adjusted that down a little bit with the idle screw on the throttle body to 750 RPMs. I then took the car for a short drive and at 40 mph I shifted into neutral and the RPMs remained at 1700. I then shifted back into gear and came to a slow stop. When stopped, the idle came back to normal 750 RPMs. I then accelerated slowly to about 20 mph, shifted in the neutral and the RPMs remained at 1300.

I am lost at where to start looking now. Any thoughts?

Thanks - Kevin

How’s the throttle body look? When is the last time you cleaned it?

Is the idle steadily high?

Have you checked for vacuum leaks?

The TPS may need to be reset. There’s an “analog” way of doing it, but if you had access to a mechanic with Jag software, it could be done quick and easy.

Is the MAF clean? (Not a typical problem)

Tell us a little more about the problem.

I removed and cleaned the throttle body one year ago when this problem first came up (~500 miles ago)

Idle is steady. When I got home from my test drive, the idle remained steady at 1300

Replaced the throttle body bellows last year. A retired Jag mechanic could not find any vacuum leaks

The car ran fine for exactly one year after replacing the first ICV. When the same issue returned last week, I assumed I had another bad ICV. Replaced it today and got the results previously noted.

Is there a temp sensor somewhere in the loop that could be faulty?

Yeah, there is, it’s cheap and easy to replace. It’s #17.

It’s plausible, and worth replacing.

Thanks, There are 3 temperature sensors. Numbers 13, 17 & 18. the wiring for Number 13 is in the same loom as the wiring coming from the ICV. I was thinking that would have been my first choice to replace. I assume you are inferring that number 17, the coolant sensor is the one needing replacing. Yes?

Yes. #13 measures the incoming air temperature. Even if it totally crapped out, I don’t believe it could cause the severity of problems you are experiencing. A faulty coolant temp sensor (#17) could possibly cause that. Don’t confuse it for the Sender (#18), that could not be the cause.

Ok, but wouldn’t a faulty temp sensor cause my dash temp gauge to read high or low? I have seen no change in its readings when engine is up to temperature.

Reread the previous post. (Veekay)

The sensor reports what it sees to the ECU.

The sender reports what it sees to the dashboard.

It completely plausible that the coolant sensor has failed, and is reporting -40C coolant to the ECU, while the sender is doing just fine, reporting a pleasant 82C to you. Unfortunately the ECU is making adjustments to make up for coolant temperature that is not accurate.

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I’ll be out of town until mid next week and won’t be able to test the replacement sensor until I get back. I’ll report my findings later next week. Thanks for you feedback to this point.

Just got back from out of town and installed the replacement temp sensor - same high idle symptoms.

I went through the steps of disconnecting the ICV and reconnecting it after the engine reached normal temperature - all good at idle ~750 rpm. Went for a short drive and the idle locks in at ~2000 rpm in second gear and above. At 40 MPH, I shift into neutral and the rpm’s remain at ~2000. However, when I slow to a stop and shift into neutral, the rpm’s remain at ~750. When I slowly accelerate and remain in 1st gear and shift into neutral the rpms remain at ~750.

It seems that my idle locks in at ~2000 rpm only when driving in 2nd gear and higher.

Any thoughts?
Thanks

Idle should be at 580rpm when warm. 700 when cold.

You should check to see what the butterfly clearance is on the throttle body. Should be .002". If that’s the case, perhaps the TPS needs to be reset. Should be done with a PDU, WDS, or any diagnostic machine that has jaguar specific software on it. It can also be done manually.

That’s assuming you really do not have any vaccum leaks. The MAF is clean and reading/reporting well.

When was the last time the oxygen sensors were replaced?

My smallest feeler gauge is .006. I opened the butterfly and inserted the tab and closed the butterfly on it. It was tight so I’ll assume I am good on the clearance.

  • No vacuum leaks, double checked, triple checked. Replaced the bellows intake boot 12 months ago
  • MAF is clean but not sure how to check if it is reading correctly
  • I have no idea concerning the O2 sensors. I have only had the car for two years. It has 67K miles

If it was tight at .006, would it plausible that it is too loose? You may need to adjust that butterfly afterall.

You can play with the MAF harness to see if you can get the car to respond in any way. If the idle starts to change based on any movement at that MAF harness connector, which can get loose, or wires brittle. The way to check if the MAF is working well would require an OBD2 reader.

Your idle is high. There’s no two ways around that. I believe it’s likely the TPS, except for your 2,000RPM issue. I still think you need it reset, since thats what most often cured all my idle issues. I could be wrong, but my next guess would be those oxygen sensors. They’re most likely original. At 67k miles, they’re due. Would be nice to see what the LTFT value is on the car.

Last question, does the car run differently when cold?