Idling issues
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Joined: Sep 2020
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From: Roberts, ID
Idling issues
My newly acquired 1990 V12 is a driver with some issues that I'm trying to figure out.
These are 2 videos that show the idling changes when the car is started and then a couple of minutes of running and then the idling does this up and down RPM from 600 to 2000, but it can be driven but when it comes to a full stop it goes back to the up and down idling. I don't really want to go down a lot of rabbit holes and mess it up more than it is now as it does drive nicely.
Thanks in advance for you advise.
Poppa
P.S.
I'm not sure if the .mov attachments showed up if not I'll need help to add them as this is my first first forum I've been part of?
These are 2 videos that show the idling changes when the car is started and then a couple of minutes of running and then the idling does this up and down RPM from 600 to 2000, but it can be driven but when it comes to a full stop it goes back to the up and down idling. I don't really want to go down a lot of rabbit holes and mess it up more than it is now as it does drive nicely.
Thanks in advance for you advise.
Poppa
P.S.
I'm not sure if the .mov attachments showed up if not I'll need help to add them as this is my first first forum I've been part of?
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Joined: Jan 2013
Posts: 5,250
Likes: 3,509
From: Calgary, Canada
Almost 100% it will be the Auxiliary Air Valve (AAV) on the left rear water rail. That controls idle speed, and has an aluminium piston and a wax capsule to move the piston, very similar to a thermostat. Over time, the piston corrodes in the bore and can't move. There used to be rebuild kits available but not any more.
There should be a bolt on the side of the AAV, try screwing that in and see if it changes the behaviour. That bolt adjusts the airflow, and is intended to be a trim to set idle speed exactly. What is happening is there is too much air flowing past the AAV, and when the ECU sees the revs too high at closed throttle it cuts the fuel. The revs drop, fuel comes back on and revs increase and the cycle repeats. There is also a possibility that the gaps at the throttle plates are not correctly set, and/or the pushrods are not correctly adjusted to move each throttle plate exactly at the same time.
A new AAV will likely cure your problem, but be aware that they are not cheap.
There should be a bolt on the side of the AAV, try screwing that in and see if it changes the behaviour. That bolt adjusts the airflow, and is intended to be a trim to set idle speed exactly. What is happening is there is too much air flowing past the AAV, and when the ECU sees the revs too high at closed throttle it cuts the fuel. The revs drop, fuel comes back on and revs increase and the cycle repeats. There is also a possibility that the gaps at the throttle plates are not correctly set, and/or the pushrods are not correctly adjusted to move each throttle plate exactly at the same time.
A new AAV will likely cure your problem, but be aware that they are not cheap.
Thread Starter
|
Member
Joined: Sep 2020
Posts: 30
Likes: 26
From: Roberts, ID
Almost 100% it will be the Auxiliary Air Valve (AAV) on the left rear water rail. That controls idle speed, and has an aluminium piston and a wax capsule to move the piston, very similar to a thermostat. Over time, the piston corrodes in the bore and can't move. There used to be rebuild kits available but not any more.
There should be a bolt on the side of the AAV, try screwing that in and see if it changes the behaviour. That bolt adjusts the airflow, and is intended to be a trim to set idle speed exactly. What is happening is there is too much air flowing past the AAV, and when the ECU sees the revs too high at closed throttle it cuts the fuel. The revs drop, fuel comes back on and revs increase and the cycle repeats. There is also a possibility that the gaps at the throttle plates are not correctly set, and/or the pushrods are not correctly adjusted to move each throttle plate exactly at the same time.
A new AAV will likely cure your problem, but be aware that they are not cheap.
There should be a bolt on the side of the AAV, try screwing that in and see if it changes the behaviour. That bolt adjusts the airflow, and is intended to be a trim to set idle speed exactly. What is happening is there is too much air flowing past the AAV, and when the ECU sees the revs too high at closed throttle it cuts the fuel. The revs drop, fuel comes back on and revs increase and the cycle repeats. There is also a possibility that the gaps at the throttle plates are not correctly set, and/or the pushrods are not correctly adjusted to move each throttle plate exactly at the same time.
A new AAV will likely cure your problem, but be aware that they are not cheap.
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Joined: Oct 2015
Posts: 1,247
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From: Vancouver
Do you have service records for this? Above posts beat me to it...Grant being 100 hours ahead of everyone down under 
also if new-to-you I'd strongly recommend O2's they are SORELY neglected and changed my car overnight from sluggish to responsive.
We have basically the same car, O2 did wonders AAV is correct thatll do it. I'm $20,000 in so rest assured if you have issues I've been through it as have many of us lol.
also if new-to-you I'd strongly recommend O2's they are SORELY neglected and changed my car overnight from sluggish to responsive. We have basically the same car, O2 did wonders AAV is correct thatll do it. I'm $20,000 in so rest assured if you have issues I've been through it as have many of us lol.
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Member
Joined: Sep 2020
Posts: 30
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From: Roberts, ID
Great support of a newbie
Grant
Thank you so much for the well informed info on what will cure the issues i currently to my XJS it's a joy just to know I have a dream car of my younger self. Thanks again for your friendly insightful help always with a sense of humor and a reason to have a brew to calm down and enjoy the process. I'll let you know how it goes, I have to get my garage heated as it's winter here the temps are steady a single digits to highs in the 20's but I'm more motivated by the day.
Poppa Pat
P.S. Did the video's upload just what to know if I can follow instructions - tee hee
You haven't missed anything I can notice. Cheers
Thank you so much for the well informed info on what will cure the issues i currently to my XJS it's a joy just to know I have a dream car of my younger self. Thanks again for your friendly insightful help always with a sense of humor and a reason to have a brew to calm down and enjoy the process. I'll let you know how it goes, I have to get my garage heated as it's winter here the temps are steady a single digits to highs in the 20's but I'm more motivated by the day.
Poppa Pat
P.S. Did the video's upload just what to know if I can follow instructions - tee hee
You haven't missed anything I can notice. Cheers
Last edited by Poppa doing it; Dec 29, 2020 at 09:26 PM.
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Joined: Sep 2020
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From: Roberts, ID
Thanks
I'm enjoying this more than I expected and it gives me motivation to get off my ***.
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I'm enjoying this more than I expected and it gives me motivation to get off my ***.
Updates to follow
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You'll be wheeling that thang around before you know it!
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