Idle speed varies - HELP
Discussion
Hi all,
For quite a while now I've had a problem that appears randomly so I haven't given it a lot of thought other than muttering "bloody thing".
1) When I come to a halt sometimes, the idle will rev at 1500 rpm for perhaps 3 or 4 seconds before dropping down relatively slowly to the normal 1000. This happens most often when I've been pressing on a bit, or the average driving revs (like in town) have been higher because of stopping and starting at roundabouts and junctions. However, sometimes it just happens when driving normally.
2) Also, I don't know whether this is linked but many times when I start the car up it seems to rev a bit too much (up to 2500 for e.g.), sounding like I'm doing it on purpose to attract attention, before dropping to normal idle.
3) Other times it will do the same as 2, but stick at the highest revs... so... key turned into ignition, car immediately revs to 2500 and stays there. Prodding the accelerator pedal usually clears it, sometimes it just idles at the increased revs!
If I get the first problem, usually I can just engage the clutch again, bringing the engine speed down and then it's usually fine. Sometimes it sticks when driving along, so I can be maintaining speed in gear while not actually touching the pedal, like cruise control. Obviously, this is not a good thing!
I've checked the throttle cable which is about 3 years old now and it seems fine. The throttle springy bit on the engine seems to move smoothly, there's no debris in it. I don't touch the accelerator when starting so it's not getting stuck behind carpet etc.
I would assume it has something to do with whatever controls the idle speed getting confused about road speed perhaps. I'm clueless really, so I'm hoping someone can give me some simple things to check...
Thanks for reading.
For quite a while now I've had a problem that appears randomly so I haven't given it a lot of thought other than muttering "bloody thing".
1) When I come to a halt sometimes, the idle will rev at 1500 rpm for perhaps 3 or 4 seconds before dropping down relatively slowly to the normal 1000. This happens most often when I've been pressing on a bit, or the average driving revs (like in town) have been higher because of stopping and starting at roundabouts and junctions. However, sometimes it just happens when driving normally.
2) Also, I don't know whether this is linked but many times when I start the car up it seems to rev a bit too much (up to 2500 for e.g.), sounding like I'm doing it on purpose to attract attention, before dropping to normal idle.
3) Other times it will do the same as 2, but stick at the highest revs... so... key turned into ignition, car immediately revs to 2500 and stays there. Prodding the accelerator pedal usually clears it, sometimes it just idles at the increased revs!
If I get the first problem, usually I can just engage the clutch again, bringing the engine speed down and then it's usually fine. Sometimes it sticks when driving along, so I can be maintaining speed in gear while not actually touching the pedal, like cruise control. Obviously, this is not a good thing!
I've checked the throttle cable which is about 3 years old now and it seems fine. The throttle springy bit on the engine seems to move smoothly, there's no debris in it. I don't touch the accelerator when starting so it's not getting stuck behind carpet etc.
I would assume it has something to do with whatever controls the idle speed getting confused about road speed perhaps. I'm clueless really, so I'm hoping someone can give me some simple things to check...
Thanks for reading.
V8S said:
I did
All I could find for the V8 was the stepper motor thing from Tinks. I don't even know where that is, let alone how to clean it
Those symptoms on the V6 would suggest the Idle Speed Control Valve (which is a different name for what is essentially the same thing). I don't know where the V8 stepper motor is either, sorry, but I think that cleaning or replacing that is probably the answer (or at least the first step towards the answer).All I could find for the V8 was the stepper motor thing from Tinks. I don't even know where that is, let alone how to clean it
I had exactly the same symptoms on my V8s. I cleaned the stepper motor on several occasions but it did not seem to make any difference. The problem happened intermittently and occasionally it was unable to select reverse or first gear without turning the engine off. I sold the car after a couple of years and never found a solution.
The steeper motor is at the top of the engine, on the off side at the rear behind the plenum, you need to be careful when you clean it, the bible covers cleaning in detail.
The steeper motor is at the top of the engine, on the off side at the rear behind the plenum, you need to be careful when you clean it, the bible covers cleaning in detail.
I had this. Quite worrying when you are slowing down in say 4th to a junction and the car surges forward again using the torque when you are expecting it to slow.
Mine is now fixed, but apologies I can't tell you what extactley fixed it but here was my process.
1) Cleaned Stepper
2) Bought myself a multimeter and snipped the two wires from then throttle pot so I could test the voltage, I set it to 0.35v after some adjustment of the mounting holes and reconnected.
3) I actually bought a new AFM though I'm convinced this wasnt part of this problem, but worth setting yours up with the multimeter (I went for 1.25v for my non cat car).
4) Screwed the idle adjust all the way in and 2 1/2 times out though apparently this is diferent for every car.
My idle was improved, no surging, stalling run-on. 2 and 3 sound more complicated than they are but see RPI's website for a how to: http://www.v8engines.com/carbs-2.htm#setting-up
I'm not even sure if some of these things are relevant but it worked for me!
Also do some searches on the Chim room, they have loadsa info on this.
Mine is now fixed, but apologies I can't tell you what extactley fixed it but here was my process.
1) Cleaned Stepper
2) Bought myself a multimeter and snipped the two wires from then throttle pot so I could test the voltage, I set it to 0.35v after some adjustment of the mounting holes and reconnected.
3) I actually bought a new AFM though I'm convinced this wasnt part of this problem, but worth setting yours up with the multimeter (I went for 1.25v for my non cat car).
4) Screwed the idle adjust all the way in and 2 1/2 times out though apparently this is diferent for every car.
My idle was improved, no surging, stalling run-on. 2 and 3 sound more complicated than they are but see RPI's website for a how to: http://www.v8engines.com/carbs-2.htm#setting-up
I'm not even sure if some of these things are relevant but it worked for me!
Also do some searches on the Chim room, they have loadsa info on this.
Edited by V8ish on Friday 11th April 11:41
Edited by V8ish on Friday 11th April 11:43
Harry1972M said:
Thanks for the link, forgot to check there!V8ish said:
2) Bought myself a multimeter and snipped the two wires from the throttle pot so I could test the voltage, I set it to 0.35v after some adjustment of the mounting holes and reconnected.
Excuse ignorance but is 0.35v the recommended standard setting? I didn't even know you could set up the throttle pot.V8ish said:
4) Screwed the idle adjust all the way in and 2 1/2 times out though apparently this is diferent for every car.
I'll look in the Bible tonight about that, thanks, and about the AFM. Thanks for the V8 link.Anyone know where to get a washer for the stepper motor? What size?
clarenceboddiger said:
Just a thought, if it was a small air leak into the intake system which may only be high enough to have any effect on (higher vacuum) overrun or once off tickover speed,my reasoning being that if you can force the revs down they stay there, clutching straws but food for thought.
yes that sounds familar Ken, I think Graham had a similar problem (V6) and it turned out to be a holed brake servo which was causing the vacuum problem, worth checking for leaks in the servo and in the vacuum hose to the servo...K
tubbystu said:
My V8S has soem idle speed moments when it needs no more than a pint or so of water / anti-freeze in the swirlpot.
God knows why, perhaps its just saying
"
a'hem I need a drink" 
Worth a look maybe ?
Don't you just love 'em
More likely it's a sensor saying "How the fGod knows why, perhaps its just saying
"
a'hem I need a drink" Worth a look maybe ?
Don't you just love 'em
do you expect me to tell the ECU what the water temperature is, when I'm not even touching the water?" followed by the ECU saying "well it must be cold then..."Well, got the stepper motor off. Decoked it and the inner bit it screws into - wasn't that dirty really - and replaced but having started the car up it's still a bit revvy on idle. Whether that's cos it's still on choke, I dunno.
Haven't driven it to find out for sure, so I will keep an eye on it on the way down to the drag racing tomorrow if the weather's ok.
Haven't driven it to find out for sure, so I will keep an eye on it on the way down to the drag racing tomorrow if the weather's ok.
Just an update.
Took throttle pot out and it was clean. Plenum looked fine, butterfly valve thingy looked clean. Hoses seem ok but there's lots and I don't really know what I'm looking for. Water in swirl tank is fine.
Still getting same problem, if not worse.
So the list of stuff still to find out about is:
AFM, road speed sensor.... and...?
Took throttle pot out and it was clean. Plenum looked fine, butterfly valve thingy looked clean. Hoses seem ok but there's lots and I don't really know what I'm looking for. Water in swirl tank is fine.
Still getting same problem, if not worse.
So the list of stuff still to find out about is:
AFM, road speed sensor.... and...?
I had same problem on mine and all simple checks for leaks, blockages, dirt, bad connections etc were good. I replaced the temperature sensor (for ECU, not the gauge) as that was only about £5, but no improvement. Cleaned stepper and checked that stepper was "buzzing" when first switching on ignition. A replacement stepper was about £100 so I was reluctant to just replace it. I then borrowed a known working stepper motor and everything was then perfect. At that point I had to fork out and buy a new stepper (which came marked "Made in Mexico"!). That did the trick and has been fine for years since.
I suggest that you also try to borrow a working stepper to see if that fixes it. Even though my stepper seemed to be working, evidently it was erratic in some way.
I suggest that you also try to borrow a working stepper to see if that fixes it. Even though my stepper seemed to be working, evidently it was erratic in some way.
On my V8S (before I took it to bits) I used to have an idle speed problem which I think is also described above.
If I turned the engine off then fairly quickly restarted it it would rev up to about 2500 rpm and even if you revved it it would refuse to reduce below this initially, and then only slowly would it settle back down to a normal idle.
I put this down to it throwing loads of fuel into the engine for the start, and probably some fuel remaining in there as I'd just turned it off. This however was a total guess. I just put up with it (& the looks!)
If you left it for a few minutes & then started it, it was fine.
There is something I think you can try with the stepper - if you get the engine running and warm at a normal idle - unplug the stepper and leave it disconnected. The stepper will then stay in the position for a normal warm idle speed. This means it will have a tendency to stall when cold as it won't increase the idle speed to compensate, but for experimental purposes warm the car through first (possibly having to blip the throttle) before driving off if you're worried about it stalling when cold.
Personally I think the stepper idea is a bit crap as it seems very slow to react anyway, but thats old technology I guess.
Chris
If I turned the engine off then fairly quickly restarted it it would rev up to about 2500 rpm and even if you revved it it would refuse to reduce below this initially, and then only slowly would it settle back down to a normal idle.
I put this down to it throwing loads of fuel into the engine for the start, and probably some fuel remaining in there as I'd just turned it off. This however was a total guess. I just put up with it (& the looks!)
If you left it for a few minutes & then started it, it was fine.
There is something I think you can try with the stepper - if you get the engine running and warm at a normal idle - unplug the stepper and leave it disconnected. The stepper will then stay in the position for a normal warm idle speed. This means it will have a tendency to stall when cold as it won't increase the idle speed to compensate, but for experimental purposes warm the car through first (possibly having to blip the throttle) before driving off if you're worried about it stalling when cold.
Personally I think the stepper idea is a bit crap as it seems very slow to react anyway, but thats old technology I guess.
Chris
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