Can't idle, won't idle
Discussion
An intermittent problem (which first manifested itself to and from the Hampshire meet last week and then went away) has today become a 'hard' problem. To and from Swindon today, my 4.0 hot-wire has refused to idle at all (both hot and cold).
The symptoms are that, regardless of engine speed beforehand, the revs decline past the usual idle speed of 800rpm, stutter around 400 and then (generally) die.
A bit of throttle keeps them at the 800-1,000 mark with no other trouble, but I didn't have my 'heel and toe' shoes on so slow traffic was a bit of a headache.
Everything else appears OK, she revs freely throughout the band, no misfires at any revs, pulls easily from 1,200 in 5th ...
Grateful for ideas on where to look.
Streaky
The symptoms are that, regardless of engine speed beforehand, the revs decline past the usual idle speed of 800rpm, stutter around 400 and then (generally) die.
A bit of throttle keeps them at the 800-1,000 mark with no other trouble, but I didn't have my 'heel and toe' shoes on so slow traffic was a bit of a headache.
Everything else appears OK, she revs freely throughout the band, no misfires at any revs, pulls easily from 1,200 in 5th ...
Grateful for ideas on where to look.
Streaky
Nacnud said:Pipes to/from plenum:
Mine had a really bad idle which was traced to a pin-hole in the tubing between the airflow meter and the plenum. There's a trick to test for a hole, squirt WD40 (or something, somebody please conform...) over the pipe and listen for a rise in engine revs.
Thin pipe to vacuum advance (from top front of plenum).
3/4" OD pipe to PAB (from outlet at bottom rear of plenum).
3/4" OD pipe - Blanked (from corresponding outlet at bottom front of plenum).
3/4" OD pipe to breather (from area of transition from intake hose to plenum).
2 X 3/4" OD pipe to water (from area of transition from the intake hose to plenum).
3/4" OD 'lazy S' shaped pipe from area of transition of the intake hose to the plenum to a protrusion from at the top rear of plenum with some electrics coming out from the other end of the protrusion.
A thin pipe immediately underneath the above protrusion which goes to a pressure valve (?) in the fuel rail.
There is a Lucas box just after the air filter labelled 'Air flow meter' but there are only electrics coming out, no pipes to/from the plenum.
So I'm a tad puzzled. I don't have the requisite books to hand for technical descriptions of the above, so hope the detail is adequate for your understanding.
Your continuing help appreciated. Many thanks.
Streaky
mungo said:Humm! There is no screw on mine, so no adjustment possible that way (equaly, no going out of adjustment either) - Streaky
Just a quick one before I shoot off tonight - I am in no way technical but this happened in my old wedge once.... is the screw on the top of the plenum chamber adjusted right??? [snip]
Streaky the base idle on the hotwire systems is 400/500 rpm. Above this to maintain it at the 1K mrk it uses a ECU controlled stepper motor, this is the elctrical gizmo you spotted attached to the end of the plenum where the last 3/4 hose on your list goes.
Switch off ignition
, remove electrical plug from stepper, unscrew stepper from back of plenum & clean it (carb cleaner is easiest), clean stepper housing as well, screw back together and try it.
If this doesn't get it up from the 400 rpm mark I would suggest you may have a more complex problem that may need a specialist to look at.
BTW the screw that macnud was on about is the one that sets the base idle, if you look to where the hose that goes around to the stepper comes from to the side of the throttle part of the plenum you will see a recess on top(could have a plastic bung in it) inside there is a allen screw which sets the base idle. With the stepper hose fully clamped (i.e. blocked off) the idle should drop to around 500rpm, if not adjust the screw, as a rough guide it should be (but not always) around 2.5 turns away from fully-in.
I hope this helps and as per usual AIMHO
Harry
Switch off ignition
, remove electrical plug from stepper, unscrew stepper from back of plenum & clean it (carb cleaner is easiest), clean stepper housing as well, screw back together and try it. If this doesn't get it up from the 400 rpm mark I would suggest you may have a more complex problem that may need a specialist to look at.
BTW the screw that macnud was on about is the one that sets the base idle, if you look to where the hose that goes around to the stepper comes from to the side of the throttle part of the plenum you will see a recess on top(could have a plastic bung in it) inside there is a allen screw which sets the base idle. With the stepper hose fully clamped (i.e. blocked off) the idle should drop to around 500rpm, if not adjust the screw, as a rough guide it should be (but not always) around 2.5 turns away from fully-in.
I hope this helps and as per usual AIMHO
Harry
HarryW said:Ah ha! That screw - taht appears large enough to bolt the engine to the floor! I was looking where part of the throttle mechanism bears on the plenum chamber when closed. There is a little 'pip' there. Just about where you might expect the idle adjustment screw for a carburetor to be.
[snip]
BTW the screw that macnud was on about is the one that sets the base idle, if you look to where the hose that goes around to the stepper comes from to the side of the throttle part of the plenum you will see a recess on top(could have a plastic bung in it) inside there is a allen screw which sets the base idle. With the stepper hose fully clamped (i.e. blocked off) the idle should drop to around 500rpm, if not adjust the screw, as a rough guide it should be (but not always) around 2.5 turns away from fully-in. ...
streaky said:
See also : www.pistonheads.com/gassing/topic.asp?t=51551&f=12&h=0
Streaky if you have a electrical feed to the speedo then it also feeds the ECU on Hotwire cars, this lets the ECU know that you are still moving.
As an example; when you take your foot off the gas the ECU sees the change in throttle pot voltage to apparent idle postion, but because it 'sees' road speed it then 'knows' you are changing gear or slowing down so keeps the revs up to around 1500. If however it doesn't see road speed it could possibily confuse the ECU. This time when it sees no throttle pot voltage as before it can't work out why the revs are still high
, you know you are slowing down engine braking/changing gear etc but the ECU doesn't, so what it (ECU) does is try to adjust the fuel and or the stepper to get the revs down to idle but it can't. What normally happens next is as you pull up to a junction the engine cuts out (this is a classic symptom for both road speed sensor and or the stepper being 
ed/dirty btw, although it odes just sometimes happen on good set up but not every time ). If this speed signal is missing from the ECU when you first start the car and you are stationary it has NO affect on the idle, it only affects it on the move.
A rough check that the speed sensor voltage is reaching the ECU is to knock it into neutral on the move take your foot off the gas, it (ECU) should keep the revs up to around 1500rpm(ish), if it (speed signal) is missing then it will go straight(ish) to normal idle (1K) or even cut out.
Usual discalimers......... AIMHO etc......
Harry
PS I think that makes sense, let me know if it doesn't
OK, an update.
Removed and cleaned stepper motor (using carb cleaaner) and inside housing. The Haynes Range Rover manual mentions a washer, but there was no washer there when I unscrewed the motor. I presume this is a fibre washer rather than a metalic one ???
I reassembled (without a washer as I did not have one the right size) and the problems remains.
Tested for a pin-hole between the AFM and plenum - no rise in revs when spraying around with lighter fluid.
It's OK at cold, the problem manifests itself as the temperature rises.
Looking for more ideas ... please?
Streaky
Removed and cleaned stepper motor (using carb cleaaner) and inside housing. The Haynes Range Rover manual mentions a washer, but there was no washer there when I unscrewed the motor. I presume this is a fibre washer rather than a metalic one ???
I reassembled (without a washer as I did not have one the right size) and the problems remains.
Tested for a pin-hole between the AFM and plenum - no rise in revs when spraying around with lighter fluid.
It's OK at cold, the problem manifests itself as the temperature rises.
Looking for more ideas ... please?
Streaky
I think a dead stepper motor would cause those symptoms. Normally, you can hear the stepper motor work briefly for about a second after you switch the engine off. This is normally drowned out by the noise of the engine spinning down, but if you just flick the ignition on and off you can hear it. If you don't hear it, I'd suspect a wiring fault or duff stepper motor.
One thing you might try to keep you going while you track down the problem, is raise the base idle to something the engine will actually idle at. It might be a bit temperamental until it's warmed up, but in principle it works fine with a fixed idle (I've run like this for a few weeks). The base idle is controlled by a screw on top of the throttle housing. If you squash the bypass hose from the throttle housing to the stepper motor assembly, the revs should drop to the base idle speed (somewhere around 400-500 rpm). If the revs don't drop, this confirms the stepper motor is jammed closed but doesn't explain why). If the base idle speed is too low the engine will eventually stop, screw the adjuster out until it keeps idling, you might need to blip the throttle a little to keep the engine running while you do this.
If you raise the base idle speed to keep you running without the stepper motor control, you will need to set it back to the proper level if you want to investigate the stepper motor problem and also when you finally sort the problem out - this is just a temporary bodge to keep you on the road in the mean time. The stepper motor will only work properly if the base idle is set correctly (roughly 500 rpm, can't remember the exact figure).
Hope this helps,
Peter Humphries (and a green V8S)
One thing you might try to keep you going while you track down the problem, is raise the base idle to something the engine will actually idle at. It might be a bit temperamental until it's warmed up, but in principle it works fine with a fixed idle (I've run like this for a few weeks). The base idle is controlled by a screw on top of the throttle housing. If you squash the bypass hose from the throttle housing to the stepper motor assembly, the revs should drop to the base idle speed (somewhere around 400-500 rpm). If the revs don't drop, this confirms the stepper motor is jammed closed but doesn't explain why). If the base idle speed is too low the engine will eventually stop, screw the adjuster out until it keeps idling, you might need to blip the throttle a little to keep the engine running while you do this.
If you raise the base idle speed to keep you running without the stepper motor control, you will need to set it back to the proper level if you want to investigate the stepper motor problem and also when you finally sort the problem out - this is just a temporary bodge to keep you on the road in the mean time. The stepper motor will only work properly if the base idle is set correctly (roughly 500 rpm, can't remember the exact figure).
Hope this helps,
Peter Humphries (and a green V8S)
jmorgan said:I used PTFE tape on the threads.
Just had a simular problem. It was the bump stop(?) under the throttle linkage. Turned it out a turn and its stopped stalling. Had to re fettle the idle as I thought it was that. Also when mine is serviced he always uses sealant on the stepper motor if its removed.
GreenV8S said:Is that clockwise (ie. down/tighten) or anti-clockwise (ie. up/loosen)? Recommendation is to tighten fully and back off 2.5 turns. Do I need to back off more or less than this?
[snip]One thing you might try to keep you going while you track down the problem, is raise the base idle to something the engine will actually idle at. It might be a bit temperamental until it's warmed up, but in principle it works fine with a fixed idle (I've run like this for a few weeks). The base idle is controlled by a screw on top of the throttle housing. If you squash the bypass hose from the throttle housing to the stepper motor assembly, the revs should drop to the base idle speed (somewhere around 400-500 rpm). If the revs don't drop, this confirms the stepper motor is jammed closed but doesn't explain why). If the base idle speed is too low the engine will eventually stop, screw the adjuster out until it keeps idling, you might need to blip the throttle a little to keep the engine running while you do this. [snip]
Many thx - Streaky
All the way in clockwise then out 2.5 turns anti-clockwise puts it in the start position for setting up the base idle of around 500rpm, it could be a turn either way away form this IMHO.
As Peter has said, perhaps you should raise it (anti-cw) a little more to stop it stalling until you get a permanent solution.
Harry
As Peter has said, perhaps you should raise it (anti-cw) a little more to stop it stalling until you get a permanent solution.
Harry
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