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This may be a wild goose chase, but your thread reminds me of a long thread on the Jag-Lovers forum a few years ago about an X300 with half the coils cutting out. After months of diagnosis by a very knowledgeable professional Jag mechanic, it turned out that the crankshaft position sensor (CKPS) was beginning to fail but had not failed completely. All that to say, if your scan tool can see the CKPS signal, it would be worth monitoring it under various engine operating conditions.
I have received the car back from the garage, it is early days but its issues seem resolved.
Whilst there:
Crank position sensor replaced - had no impact on the car (but not a bad thing to change given the age of car)
Reset adaptions for throttle body as this had been previously cleaned.
ECU showed no faults.
Each coil test on oscilloscope - no change in firing image on any coil when any misfire occurs.
As is sadly often the case, I have spoken too soon. The weekend here was warmer than recent and during that period I did not experience the oscillating revs at idle. However, today we are back to winter and sadly on the new plugs oscillating revs are back, but not as bad as once was the case, but there nonetheless.
If a change of plugs has improved things, I am tempted to go back to trying some used original Lucas coils. I will install them this weekend. If all then remains the same I think going to a proper Jag specialist is my next step.
Please do the manual IACV reset. It doesn’t work permanently, but let’s see if it fixes it at least temporarily?
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.
If the car idles smoothly now, it is likely the IACV. Unfortunately, once you turn the car off and back on, I believe whatever this process does to the IACV....it gets lost, so you’ll be back to square one. At least we might learn something? If it continues to oscillate, it is not the IACV.
I recall that Lady P, Vee and others have mentioned the Idle Air Control Valve (IACV). Have you cleaned the throttle body (TB), throttle position sensor (TPS) and IACV?
Another thought is that the IACV works together with the carbon canister purge valve to help maintain smooth idle while the canister is purging. If the purge valve is stuck open, it behaves like an intake air leak. I can't recall whether you've checked the purge system.
The X300 OBDII system is somewhat primitive and may not detect small leaks in the EVAP system.
Vee this weekend when I have some free time to work on the car I will do the IACV reset test.
Don thanks for your thoughts. To answer the throttle body (TB) has been cleaned and the adaptions reset afterwards. The TB was very dirty. The throttle position sensor (TPS) was tested by my mechanic and found to be functioning correctly.
I do not believe the IAVC has been cleaned/tested/replaced. So that seems to be the next step.
Any guidance on what to do beyond/as well as Vee's suggested test would be much appreciated.
Spray with penetrate the IAC bolts before hand as they do break ( locktited ) and can be removed without removing the TB with a thin wall 6 not 12 point 5.5 or 6.5 metric socket . Look for the TBS to read on the middle wire 0.60 + or - 0.02 volts at the idle stop . Don't adjust the TPS yet till further advised . If you want to read the IAC valve step motor with a meter you would have to read the 1 to 1 and 2 to 2 pins one set at a time and see that each leg has the same resistance as you tap on it to see it open simulating heat expansion opening a broken winding wire . . The connector has no ECU feedback position agreement wires to the ECU so all 4 pins are motor driving wires .
Last edited by Lady Penelope; 02-19-2018 at 01:39 PM.
I recall that Lady P, Vee and others have mentioned the Idle Air Control Valve (IACV). Have you cleaned the throttle body (TB), throttle position sensor (TPS) and IACV?
Another thought is that the IACV works together with the carbon canister purge valve to help maintain smooth idle while the canister is purging. If the purge valve is stuck open, it behaves like an intake air leak. I can't recall whether you've checked the purge system.
The X300 OBDII system is apparently somewhat primitive and may not detect small leaks in the EVAP system.
Cheers,
Don
If the Rochester Valve has failed, would that cause a similar situation?
The OEM part no longer exists, but ACDelco 214-552 works.
Would that be tested with a simple common code reader in the EVAP system test mode being no electrical connector and requiring engine running for muscle air to actuate ?
If the Rochester Valve has failed, would that cause a similar situation?
The OEM part no longer exists, but ACDelco 214-552 works.
If the canister pressure control valve/close valve/shutoff valve/vacuum control valve (a.k.a. the "Rochester Valve") sticks open, it allows ambient air into the system when it shouldn't, so yes, that could certainly cause problems.
Would that be tested with a simple common code reader in the EVAP system test mode being no electrical connector and requiring engine running for muscle air to actuate ?
I seem to recall that at least one Rochester valve failure mode will trigger a DTC, but I can't remember if it's "stuck closed" or "stuck open." A vacuum pump is the common method of testing the valve.
If my car requires a new IACV is it true that a Renault part will work? I have seen an old forum post for XJ40.com from our very own katar83, which mentions part number D95174 from Renault. Would this be the same item on a XJR as on a NA car?
Or instead of saving 40 or so Pounds would it be best to get a Jaguar dedicated one - the people from worldcarparts who do the aftermarket MAF sell one.
Could a faulty IACV lead to overfuelling and blackening of spark plugs?
Correct on the renault part and my post on the xj40.com forum, I'm using one atm too IACV is the same for XJR and normal XJ.
I don't think the IACV will be your problem though, its also a pain to get it out as the little bolts are very hard to get to(at least one of them), they will possibly snap at first turn so you might have to drill them out(which means TB out). IACV can be tested too and you can always disconnect it when its 'parked' see how the car works without it(when warm though). It only works/is used when the car is idling.
Item # 9 showing aft of the single carbon canister system on the left side . There is earlier X300 EVAP system that has 2 canisters one on each side with no Rochester valve ( ? )
I also installed a Renault Megane IACV stepper motor in our '93 XJ40/AJ6. The large images are still down, but you can see my thumbnails and descriptions here:
However, I don't think this part will fit an AJ16/X300. The motor housing and mounting screw orientation appear to be different. Below is a photo of the AJ16/X300 IACV, part LNA1500AB, courtesy of SNG Barratt, which you can compare to the photos of the Megane IACV motor in my photos at the link above:
EDIT: katar83 is right, I grabbed the wrong part off of SNG Barratt. The above is a photo of one of two IACVs on the 12-cylinder engines. Here's the diagram for the S/C 6-cylinder engines, in which the stepper motor, Part 15, does appear to resemble the one on the XJ40 and Renault Megane:
Nick, I would personally recommend you remove and clean your IACV and stepper motor and the port in which the plunger operates. Ours was so heavily carboned that it couldn't close completely. Clean the plunger with a small wire brush and throttle or carb cleaner and use a battery terminal wire brush to clean the port in the throttle body and flush it out with throttle body cleaner. I will be surprised if this doesn't help at least a little.
I don’t know about IACV interchangeable parts, but I do know that there is a squishy orange gasket that I replaced on my IACV which helped resolve a vacuum leak... It happened to be a size I already had lying around, 5/8” diameter maybe? You’ll want to make sure that gets addressed.
Black spark plugs are usually a result of oxygen sensor issues, but you said you swapped those out already?
There was a changeover to teflon seals in the step motor only ( not the TB mounting to valve body ) to keep stuff out of it and it's preferred to have the motor oriented so Carb cleaner doesn't flush in .
The X300 IAC is the cylindrical one as the other will not fit .
Lets not overcomplicate things, the part number JLM12185 is a stepper motor for XJ and XJR according to JCP and I believe we're talking about the same thing. I don't even know what LNA1500AB is and I think this will be an IACV for the V12 x300 or something to do with the water rail on v12?
I suspect removing IACV on XJR is going to be a major job with the supercharger in the way. I would hope that whoever cleaned up the TB cleaned up the IACV at the same time too since they are bolted together. Also like I said, its easy to check, just warm up the car, unplug when IACV is parked, see whether this improve things. I suspect it wont.
I'd concentrate on coils, then o2 sensors and then injectors.
02-16-2018, 09:04 AM
IACV is the same for XJR and normal XJ.
