Weird surging idle after battery change
#1
Weird surging idle after battery change
On my 45k mile 1990 US spec XJ40 4.0
We changed the battery and the oil and filter. First few starts and idles it was fine. Then it starts with this nonsense.
Car was for sale and is actually now sold...... on its way to new owner on Friday, so would be kind of handy if it ran properly by then.
It behaves like a vacuum leak, but the fact that it can sometimes just go away on its own, or sometimes goes away after a restart makes me think its not a vacuum leak, more like an electrical ECU type issue after the battery change.
I've changed the battery before and didn't do anything special to recover it (apart from retraining the alarm remotes) and I never came across this issue until now. Maybe I was "lucky" previously.
No Check Engine light. No codes in the VCM.
We changed the battery and the oil and filter. First few starts and idles it was fine. Then it starts with this nonsense.
Car was for sale and is actually now sold...... on its way to new owner on Friday, so would be kind of handy if it ran properly by then.
It behaves like a vacuum leak, but the fact that it can sometimes just go away on its own, or sometimes goes away after a restart makes me think its not a vacuum leak, more like an electrical ECU type issue after the battery change.
I've changed the battery before and didn't do anything special to recover it (apart from retraining the alarm remotes) and I never came across this issue until now. Maybe I was "lucky" previously.
No Check Engine light. No codes in the VCM.
Last edited by Sarc; 05-02-2019 at 01:40 AM.
#2
Resetting by disconnecting the battery cables and shorting them out, then starting from cold and waiting for warm up then driving made it slightly better.
When it is bouncing around if I shift it into drive that pulls the idle down then back in to park and it's fine.
So I have an idle problem, not a vacuum problem. My gut feel is if I just drive the thing for a while it'll short itself out, but that's not a great story for the excited new owner.
Next thought is to clean the throttle body and intake manifold........
Any other inputs welcome at this point
When it is bouncing around if I shift it into drive that pulls the idle down then back in to park and it's fine.
So I have an idle problem, not a vacuum problem. My gut feel is if I just drive the thing for a while it'll short itself out, but that's not a great story for the excited new owner.
Next thought is to clean the throttle body and intake manifold........
Any other inputs welcome at this point
Last edited by Sarc; 05-02-2019 at 11:15 AM.
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Don B (05-03-2019)
#3
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Don B (05-03-2019)
#6
Check the connection at your IAC motor. It will relearn where the piston can be but it should go away relatively quick. Seems like you may have a spotty connection if it is intermittent. Did you wash the engine compartment or anything like that since you are trying to sell it?
To add more detail to my second post, and also to bolster Larrys idea, I only drove the car about 300 yards after doing the reset........ I'm thinking this is not enough so will go drive it more.
But, I will check the connector and clean it anyway. We were changing oil, swinging batteries in and out, etc so there's always a chance of something getting knocked
#7
So..... We did a lot of driving with the car today and all appeared well, but then after sitting for 3 hours, at restart the idle bouncing returned.
After a few key off and ons, everything returned to normal.
I inspected and cleaned the IAC connector. All looks ok.
Puzzled.......
After a few key off and ons, everything returned to normal.
I inspected and cleaned the IAC connector. All looks ok.
Puzzled.......
Last edited by Sarc; 05-02-2019 at 10:42 PM.
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#9
Have a read of this thread Sarc, stepper motor setups for the different motors
https://www.jaguarforums.com/forum/x...e-idle-118636/
Larry
https://www.jaguarforums.com/forum/x...e-idle-118636/
Larry
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Don B (05-03-2019)
The following users liked this post:
Don B (05-03-2019)
#12
#13
The idea is to drain the capacitors in the ecu of any residual charge that could prevent the ecu from forgetting some settings that you *might* want to erase.
Larry
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Don B (10-28-2019)
#14
This is called a hard reset, you just have to undo the neg terminal and hold it to the positive cable. The positive terminal doesn't have to be disconnected from the battery as the battery is out of the circuit with the neg terminal off.
The idea is to drain the capacitors in the ecu of any residual charge that could prevent the ecu from forgetting some settings that you *might* want to erase.
Larry
The idea is to drain the capacitors in the ecu of any residual charge that could prevent the ecu from forgetting some settings that you *might* want to erase.
Larry
#15
#16
#17
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Hi Mike,
I replied with a few ideas in your thread at the XF forum.
Cheers,
Don
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