Jaguar x300 cuts out at junctions but runs fine when normal driving along the road. Also hesitates a bit when setting off again. Regards, Robert.
So is this an idle problem? Or is this a problem under braking?
Usually an idle problem. When was the last time that the throttle body
was cleaned?
Chri C
HarryE30 wrote:
Does it start straight up again? If it does I would check the wiring from the CPS. My ‘40 did this and it was the shield wire shorting out the signal wire.
Yes it does start straight away, but when i press the throttle to go it hesitates for a second, then its off like a rocket.
I think I have narrowed it down to either the TPS or the ISCV. Which one is it most likely to be. Regards, Robert.
I am a little in the scolding mood this morning! You, and others, post a problem with no mention of the CEL or the OBDII diagnostic codes. Without those, it is a crap shoot with bad odds of getting it right. But maybe it is fun to guess?
Problem is there is no codes showing up in the diagnostics, could be because of the age of the car, I don’t know. I have change nearly everything else mentioned except the two items I mentioned, I’m tempted to just change the whole throttle body, as they are both on that. Regards again, Robert.
Well, if you change the throttle body, theoretically, you should do the TPS calibration. There is, of course, a chance you will hit a new one with the same calibration constant, but you will not know. If you do change the throttle body, at least use your scanner to read the throttle position at idle and WOT to see if you are in the ballpark with the new one.
I don’t know what you mean by “because of the age of the car”. The MY 95 was not fully compliant with OBDII, but you would be hard pressed to identify what is different between MY 95 and MY 96, which is compliant. I suspect it was only certification.
I would have a go at cleaning the ISCV before I changed the throttle body or the TPS. There is a fairly small passage known to clog, as I recall. A stuck open EGR valve could also mess with the idle.
A bad or one mis-calibrated TPS will more likely cause high idle rather than stalling. Try unplugging it and see what happens. A hard boot will fix any limp mode you might induce.
Good luck.
Don’t change the throttle body!
If this happens when the car is stopped or below 5mph, then it’s more likely the IACV.
What I would recommend, is pulling it out, cleaning it up, and changing the two gaskets that come with this part. One is a rubber o-ring, commonly found, the other is the dedicated gasket, part number JLM11490.
Word of advice, there is a very good chance that you will strip the screws/bolts that hold this in place, so be careful. I forgot what you’ll need, but it’s the one that’s hard to find… I want to say an M4 sized timesert, ot helicoil. If you can’t get the socket to remove the bolt dead on, don’t try to remove it at an angle.
Anyways, keep us posted on progress!
Thank you for that Veekay, I must say that the ISCV has been mentioned to me a few times as the possible cause of the problem. Would you say that the ISCV would take priority over the TPS and the MAFF sensors as the main culprit. Regards, Robert.
Only because you mention that your problems only exist when stopped or below 5mph. That’s when the IACV kicks in.
I would first replace the o-ring, since it’s easy and cheap to replace. Do be careful removing that IACV, those tiny bolts are known to shear off. Put a little sealant on the existing gasket, both sides, perhaps that can be reused, but the o-ring is likely shot.
Don’t you have an OBD2 port? You would be able to see what the car sees in terms of (1) MAF sensor readings and (2) throttle position as read by the TPS. That would help reduce the probablility of those two creating this problem.
I will warn you that when I’ve replaced my IACV, my idle went haywire and I needed to get it to a shop to get the idle reset. That’s why it might be better if you try to fix the one you have…assuming it’s only the gasket and o-ring creating this issue for you.
The reason your idle went haywire is because the TPS in the new throttle body needed calibration. The idle control only works when the ECU senses the throttle is at idle. The only valid way to calibrate the TPS is with the dealer level software.
I fully concur that the ISSC (IACV) is, by far, the most likely culprit, followed by the EGR valve.
I never replaced the throttle body, nor the TPS!
Hmmh. The IACV is self calibrating, but does not become active until the TPS detects idle throttle position. So, the only “idle reset” at the shop should have been a TPS calibration. Maybe the TPS had become miscalibrated previously? Although the manual and “common knowledge” say the TPS should not change calibration, mine became dodgy even though the TPS measured good. I assumed it was a “failing” TPS and replaced it and then learned about the TPS calibration procedure requiring WDS software. Bought the WDS unit, calibrated it, and then good idle!
The IACV is moved by a stepper motor that closes at each ignition switch power cycle to the closed (calibration) position. It then opens to the last set position and controls position using idle speed as the process variable. That is why powering the car down while the IACV is connected, but not mounted in place will result in the (rapid) ejection of the pintle.
There is a process to recalibrate the ISCV which involves disconnecting and reconnecting in a certain procedure a number of times:
http://www.jagweb.com/aj6eng/fault_codes.php
Scroll down the page to the setting procedure.
While that reference is quite interesting, it is for a Lucas 9CU ECU used on an AJ6 engine. We are (reportedly) working on an X-300, AJ16 engine which works as I described.
You know, at this point, like the others who have studied the X-300 manuals and info in depth, I will just go away and you all carry on…
I can confirm that the reset procedure you described will not work for the AJ16.
I have tried it, and it has an effect on the idle, until the car is restarted, then everything is back to where it was before.
Hmm you’ve been unusually patient and calm up to this point Ross but I concur!
A similar vien runs through other current posts.
PS causing me along with other more significant and far more KNOWLEDEABLE other Member to loose interest and become absentees or mere observers.