Idle air valve control
#1
Idle air valve control
I just developed a new condition on my 1996 XJS. My idle started to go out of control. While driving and taking my foot off the gas it would idle up instead of going down.
I disconnected the idle air control valve to see if it functioned differently. It does.....it runs better!!!! What is going on?
It is a very cold day for Florida so whenI started it up this morning to see if it would even start without the idle control valve disconnected. It started right up...idle was a little hesitenty but with warming up it ran ok.
I adjusted the the idle mechanically after it warmed up good...600 w/brake in gear and 750 in neutral. It runs really well so I took it for a spin ~ 10 miles....No issues what so ever.
Can someone please explain this to me......
I did order a new idle control valve.
Thanks as always
Softball60/Paul
I disconnected the idle air control valve to see if it functioned differently. It does.....it runs better!!!! What is going on?
It is a very cold day for Florida so whenI started it up this morning to see if it would even start without the idle control valve disconnected. It started right up...idle was a little hesitenty but with warming up it ran ok.
I adjusted the the idle mechanically after it warmed up good...600 w/brake in gear and 750 in neutral. It runs really well so I took it for a spin ~ 10 miles....No issues what so ever.
Can someone please explain this to me......
I did order a new idle control valve.
Thanks as always
Softball60/Paul
#2
They can get carboned up and stick in various stages of the operating range.
When changing the valve, be aware that the small screws that hold it to the throttle body have loctitie on them, if you try and undo them you will break off the screws. Heat them with a microtorch before trying to undo them, the heat breaks down the loctite.
When changing the valve, be aware that the small screws that hold it to the throttle body have loctitie on them, if you try and undo them you will break off the screws. Heat them with a microtorch before trying to undo them, the heat breaks down the loctite.
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kjopen (01-11-2019),
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#3
Well it has been several days and I have been driving without the idle control valve connected.
Other than the initial warmup with the higher rpm the jag has been running great.
I am a little confused that not one engine failure light has gone on. Is this more of a auto chocking device and possibly to eat out another 1/10th of a mpg?
My new unit will be here in a couple days.
Your insight is appreciated.
Thanks
Softball60/Paul
Other than the initial warmup with the higher rpm the jag has been running great.
I am a little confused that not one engine failure light has gone on. Is this more of a auto chocking device and possibly to eat out another 1/10th of a mpg?
My new unit will be here in a couple days.
Your insight is appreciated.
Thanks
Softball60/Paul
#4
The 96 is reluctant to throw out codes for much of anything. Jag had just entered the OBD2 world and didn’t get good at it until later on.
Basically, if you have a code, it helps you find the problem, but the lack of a code shouldn’t cross off any potential failure that a code would normally shed light on.
Basically, if you have a code, it helps you find the problem, but the lack of a code shouldn’t cross off any potential failure that a code would normally shed light on.
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#5
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Softball60 (01-13-2019)
#6
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Softball60 (01-13-2019)
#7
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#8
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Softball60 (01-14-2019)
#9
Malfunctioning IACV causes havoc. Disconnected IACV results in overfuelling since the car must assume the amount of air coming into the engine.
After replacing the IACV, you'll likely need to have the TPS reset, which needs to be done with someone that has access to Jaguar specific software. The dealer will always have access to that, fewer independent shops will as well. That's been the case with my AJ16 engined cars. Everytime I swapped out the IACV, the idle ran high until the TPS was reset.
After replacing the IACV, you'll likely need to have the TPS reset, which needs to be done with someone that has access to Jaguar specific software. The dealer will always have access to that, fewer independent shops will as well. That's been the case with my AJ16 engined cars. Everytime I swapped out the IACV, the idle ran high until the TPS was reset.
Last edited by Vee; 01-14-2019 at 10:34 AM.
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Softball60 (01-14-2019)
#10
#11
That manual readjustment might work on an AJ6 engine, but it will not work on the AJ16. The reset works, until you shut the car off and then whatever the manual reset did is lost and forgotten.
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Softball60 (01-15-2019)
#12
Malfunctioning IACV causes havoc. Disconnected IACV results in overfuelling since the car must assume the amount of air coming into the engine.
After replacing the IACV, you'll likely need to have the TPS reset, which needs to be done with someone that has access to Jaguar specific software. The dealer will always have access to that, fewer independent shops will as well. That's been the case with my AJ16 engined cars. Everytime I swapped out the IACV, the idle ran high until the TPS was reset.
After replacing the IACV, you'll likely need to have the TPS reset, which needs to be done with someone that has access to Jaguar specific software. The dealer will always have access to that, fewer independent shops will as well. That's been the case with my AJ16 engined cars. Everytime I swapped out the IACV, the idle ran high until the TPS was reset.
All that is needed to get IACV in fully closed position on AJ16 engine is to cycle ignition few times, generally when you switch off the engine the iacv should extend itself, then go up a little, so next time you fire it up IACV is already in partially open position and allow a bit extra air on possibly cold startup. You can always connect a spare IACV, hold it in hands(to prevent plunger shooting out of the IACV) and have someone turn ignition key two position 2, wait few seconds and go back to 0 and wait again, this should explain best how it works and how to get it fully extended so when after replacing it you shouldn't have any high idle problems.
Hope that makes sense!
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#13
Katar83,
While on paper this may work, my experience has been otherwise. I spent a good amount of my life chasing down TPS and IACV problems. Eventually, after paying Jag specialists a few times for a reset, I found my own WDS and ended that! (Now I also have a PDU, I just don't have cables for any Jaguar vehicle without an OBD2 port!)
Anyways, I agree that changing the IACV should have nothing to do with resetting the TPS, yet for some reason, everytime I have replaced an IACV, a TPS reset seems to be in order. A manual reset of the IACV seemed to fix the idle, but only until the engine was shut off.
As for manually resetting the TPS, that indeed can be done too. I forgot about that. Slotting the two bolt holes so the TPS can be adjusted, while on the throttle body, with the car idling, you can slightly adjust the position of the TPS so that it idles correctly, then you can lock it in. There are indeed threads on that too.
While on paper this may work, my experience has been otherwise. I spent a good amount of my life chasing down TPS and IACV problems. Eventually, after paying Jag specialists a few times for a reset, I found my own WDS and ended that! (Now I also have a PDU, I just don't have cables for any Jaguar vehicle without an OBD2 port!)
Anyways, I agree that changing the IACV should have nothing to do with resetting the TPS, yet for some reason, everytime I have replaced an IACV, a TPS reset seems to be in order. A manual reset of the IACV seemed to fix the idle, but only until the engine was shut off.
As for manually resetting the TPS, that indeed can be done too. I forgot about that. Slotting the two bolt holes so the TPS can be adjusted, while on the throttle body, with the car idling, you can slightly adjust the position of the TPS so that it idles correctly, then you can lock it in. There are indeed threads on that too.
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#14
#15
I'm hoping you'll come back and wrap this one up for us.
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Softball60 (01-20-2019)
#16
As a matter of fact received the IAC yesterday and installed today. A couple of trips and all. Is well. Idle in gear 600rpm and in neutral 750.
When initially started it starts out @ ~ 1100rpm and idle’s down to 750.
Everything is good!!!
Thanks to all for their involvement.
Softball60/Paul
When initially started it starts out @ ~ 1100rpm and idle’s down to 750.
Everything is good!!!
Thanks to all for their involvement.
Softball60/Paul
#17
Excellent! Happy to hear it went well.
On a related issue, perhaps my TPS was bad longer than i thought since I was chasing down a high long term fuel trim that was resolved by replacing my TPS with a new one. Maybe when i replaved my IACV, it uncovered the failing TPS which was then band-aided when i reset it using a WDS.
I learned something here. Thank you.
On a related issue, perhaps my TPS was bad longer than i thought since I was chasing down a high long term fuel trim that was resolved by replacing my TPS with a new one. Maybe when i replaved my IACV, it uncovered the failing TPS which was then band-aided when i reset it using a WDS.
I learned something here. Thank you.
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Softball60 (01-21-2019)
#18
For back yard mechanics like myself, it sometimes takes a lot of trial and error. I have come to learn two (2) things;
1. When the idle is all over the place high and low it is usually the IAC.
2. When it does not want to take off from a standstill idle it is the TPS.
I am proud to say that other than installing tires/etc. NO ONE has touched my car for any repair but Me!!!!
It is not so much how good you are, but taking advantage of all the resources available, ie; Jaguar Forum, U-Tube, etc.
It is just great having these kinds of discussions!!
Thanks as Always
Softball60/Paul
1. When the idle is all over the place high and low it is usually the IAC.
2. When it does not want to take off from a standstill idle it is the TPS.
I am proud to say that other than installing tires/etc. NO ONE has touched my car for any repair but Me!!!!
It is not so much how good you are, but taking advantage of all the resources available, ie; Jaguar Forum, U-Tube, etc.
It is just great having these kinds of discussions!!
Thanks as Always
Softball60/Paul
#19