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high idle speed

Gary Mead

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Mar 29, 2010
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need some advice on what to look look for or at???.I have just replaced the two batteries on the car as they had given up after 7 years or so,since ive done that the idle speed has risen to nearly 1000rpm (like when you put the a/c on)being an auto this makes the car want to pull away.The a/c is all still working as normal but the idle remains high if the a/c is on or off????.all the rods on the pump appear to be moving correctly,had a good look round under the bonnet but cant see anything obvious out of place.

cheers gary
 

Andrew Prince

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Feb 23, 2010
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Hmm that does sound like a strange one. Before everyone (me!) starts spouting theories, perhaps it's worth disconnecting the batteries and reconnecting again :idea:
Does the higher idle continue once the car is warmed up - i.e. when you've been for a drive and then come to a halt? I assume it's a diesel from the idle speed?

Starting to speculate (and may be way off with these thoughts!):
-Higher idle speed might point to something like the ACSD (auto cold start device) misbehaving - not sure why the battery change would prompt something like this...
- I don't think the alternator running would cause a higher idle speed but if it is the alternator, then you need to track down where the extra current draw is happening. Maybe a relay sticking on the pre-heater?
- Is the aircon working properly? I.e. the clutch is engaging/disengaging when switched off. Not 100% sure how the a/c switching works but if the clutch is packing up, maybe the compressor is still putting a load on the engine even when switched off?

[/grasping at straws]

Good luck - hopefully some smarter people than me has some insight to offer!
 

Chris

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Sounds a reasonable set of theories.

Is there a gap between the idle screw and the idle cam? If there is, then maybe it is the cold start holding it off. If the cam is on the idle screw then I would just turn the screw down a little. No I can't explain it either, but if that brings the idle back down then at least it's sorted. I have adjusted my throttle so that the cold start mechanism comes in, but does not contact the throttle cam and raise the revs at all. It was annoying and as you say, wants to push the car along. I nearly hit the lamp post opposite when I came off the drive for the first time. It just ran away with me. I found that even when I had done that and it was warm, the cam still didn't touch the idle screw. What???? I had to adjust the linkage screws to get it to reach. I think someone had been tinkering. On cold start it idled at 1500 rpm

Chris
 

zsandoe

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So my idle is sitting at 950-1000 when warm. I’ve adjusted it down to 800-850ish while running twice now with the Allen key and nut on the throttle (stop) but when I drive the car a day or two later idle is back up towards 1000. I noticed when I hit the a/c button the light comes on but there is no fluctuation in the revs. I’m wondering if the ac clutch it constantly engaged... I don’t think the a/c is blowing any colder when on so i doubt its working. Car runs fine otherwise, the idle just sits a little high. Any suggestions?
 

Towpack

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Try disconnecting the vacuum hoses to the AC and PS actuators and see if the idle speed drops slightly, then reconnect them and turn on the AC and turn the steering to see if the actuators do anything. As has been said above I also can’t see a link between a battery change and the fault. A stuck cold start (ACSD) could also cause it but it’s a purely thermo/mechanical device with no electrical connections.
 

zsandoe

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Try disconnecting the vacuum hoses to the AC and PS actuators and see if the idle speed drops slightly, then reconnect them and turn on the AC and turn the steering to see if the actuators do anything. As has been said above I also can’t see a link between a battery change and the fault. A stuck cold start (ACSD) could also cause it but it’s a purely thermo/mechanical device with no electrical connections.
So pull them when the AC is off and engine is running? Haven’t looked but is it obvious which lines exactly?
 
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Towpack

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The actuators for the AC and PS are stacked together and operate the same linkage. Can’t remember exactly which is which but it’s easy enough to identify each one. The procedure I described is just to prove that...
1. The actuators are actually working and
2. One of them isn’t stuck ‘on’.
 

zsandoe

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The actuators for the AC and PS are stacked together and operate the same linkage. Can’t remember exactly which is which but it’s easy enough to identify each one. The procedure I described is just to prove that...
1. The actuators are actually working and
2. One of them isn’t stuck ‘on’.
Where are they?
 
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