Idle Speed Motor.

[Barson]

I just need you to confirm my suspicions that my idle motor is bad.

Have a look at this:

http://homepage.ntlworld.com/drlanceangr...boutit.AVI



It's a video of me operating the idle speed micro switch.

The aperture within the idle motor isn't closing. The valve is just twitching.

With it disconnected I can move the valve manually but when connected it just twitches when in fact it's supposed to close the gap solid.

I suspect this'll be causing un-metered air entering into the manifold and possibly causing my backfiring into the intake (amongst other things)?



Hey ho
Dave.

[NickT]

Sounds like you are having fun sorting your problems out !
Let me know if I can help.

The air through the idle speed control valve is metered as the source is from the venturi.
The motor is an analogue one with 2 oppositely wound windings.
On the car, the center pin has 12v to both windings.
When you MOMENTARILY earth one of the outer pins the motor goes fully open or fully closed depending on the winding.
When you MOMENTARILY earth the other winding it should go the opposite way.
When you first turn the ignition on the ecu opens the valve fully to aid starting.
If it doesn't do that test then the motor needs replacing. The valve should be very loose in the motor for quick control.
The one from a later volvo 760 works too but is smaller so you need to change the backet or on mine don't bother with one.

When the engine is cold the thermistor under the inlet manifold gives the ecu information to raise the idle speed when cold (like a good old choke on a carburettor). Unfortunately this relationship isn't quite right so I put in an extra resistor in series with the sensor (usualy 10k ohms 1/2 watt) but this may depend on the ecu working right or not !

If your ecu doesn't work then they can be repaired for £10-15 worth of components.

NickT.

[Barson]

The thing DOES fully open on crank.
I've tested both windings and the thing does flip back and forth at you would expect.

The thing i don't understand it why the motor would be open as the idle speed switch is disengaged - shouldn't it shut and allow the venturi to meter the air as you say?

Is it the thermistor that's telling the ECU that the engine is cold so the ECU it keeping the motor open?

I'm perhaps misunderstanding the way the motor works with the engine. I thought it was ust a matter of the thing openning fully and shutting fully depending on what the idle speed switch does.

One thing I should mention is that the metering flap isn't shut on idle - it hovers just slightly downward. also with the air filter housing off the flap (or what's beneath the flap) makes an awful sucking sound like a vaccum cleaner sucking up a puddle if warm vomit.

I unplug the motor and it diappears. any ideas?

[Tourettes Tony]

i have a thermistor if you need it cheers tony TT

[NickT]

Barson Wrote:The thing DOES fully open on crank.
I've tested both windings and the thing does flip back and forth at you would expect.

The thing i don't understand it why the motor would be open as the idle speed switch is disengaged - shouldn't it shut and allow the venturi to meter the air as you say?

Is it the thermistor that's telling the ECU that the engine is cold so the ECU it keeping the motor open?

I'm perhaps misunderstanding the way the motor works with the engine. I thought it was ust a matter of the thing openning fully and shutting fully depending on what the idle speed switch does.

One thing I should mention is that the metering flap isn't shut on idle - it hovers just slightly downward. also with the air filter housing off the flap (or what's beneath the flap) makes an awful sucking sound like a vaccum cleaner sucking up a puddle if warm vomit.

I unplug the motor and it diappears. any ideas?

Sounds like ISCV is ok if you have done the tests.
The ISCV motor is position controlled by the ecu pulsing the windings quickly.
http://www.picotech.com/auto/waveforms/ ... otary.html
Using this control the valve can be positioned at any point.
If the switching rate is equal (yet anti-phase, they don't switch together) to each winding then the valve will appear stationary. If one side is switched slightly longer than the other then the valve will move in that direction accordingly.

Where this valve is positioned ie how far open or closed it should be is given by the switching rate at the ignition coil ie the rotation speed of the engine.
The engine idle speed set point is usually about 775 +/- 50 rpm
If the actual engine speed is higher than this figure then the ISCV will be control closed slowly.
If the actual engine speed is lower than this figure then the ISCV will be controlled to open slowly.

If the engine is cold then the ecu will raise the engine idle speed set point to approx 1100rpm to 1300rpm depending on the resistance of the thermisotr.

I have not seen the position of the ISCV when the throttle switch is disengaged but would have thought it would be either be positioned half open or fully closed.
I have a spare working idle speed ecu if you want to try it out.

The air through the ISCV is metered by the ventury so the fueling is correct. The air path through the ISCV comes from the brass pipe under the manifold at the back into the venturi housing and then goes past the throttle plates.

I am not sure about the noise you mention. Without listening to it myself I couldn't say if it is normal or not.
Note where your brasss screws are then wind them all in counting the turns so they can be returned to the original position.
See what effect this gives on your car. The gurgling noise may be the air by-pass through the channels past the throttle plates. The brass screws adjust the amount of air through these channels and could be wound open too far hence the sucking noise.
Worth a go. A bit hard to tell without seeing the car.

Good luck.

NickT.

[Barson]

thanks for your time in explaining this Nick

I think I will borrow the ECU from you, if you don't mind.

I can test the rest of the system with it and perhaps eliminate my ECU from my enquiries.


I understand also that it's difficult to know what's going on when you're not at the car.

I spend half my time either reading through posts (posting here), dmcnews, dmctalk, or the manuals to get a half decent understanding of what's going on. the other half of the time is spent doing my back in leaning into the engine :p

[NickT]

I'll pop it in the post tomorrow for you.
You can tell which one is mine as it is cut open from my repair and has NickT written in pencil on it.

NickT.

[steve.s]

Hi

just wandered what your fault is.

i too suspected the idle motor (and possibly still do).

i tried the 12v test.

with a jump battery the thing jumps one way or other with a clonk.

Martin tested my idle ecu and came back ok.

also, make sure the ground to it is ok, and the feed off the coil.

my car is now playing up again. struggles to start runs 30 seconds then dies.

throttle kills it quicker.

jump the cold start valve and runs then.....what is going on?.

[Rich H]

Steve, that, sounds a bit like blocked CPR to me. But I think I'm getting Deja Vu here, haven't you replaced it already....?

Try *lightly* pressing down the metering flap during tick over and see if it helps

[Barson]

steve.s Wrote:Hi

just wandered what your fault is.

i too suspected the idle motor (and possibly still do).

i tried the 12v test.

with a jump battery the thing jumps one way or other with a clonk.

Martin tested my idle ecu and came back ok.

also, make sure the ground to it is ok, and the feed off the coil.

my car is now playing up again. struggles to start runs 30 seconds then dies.

throttle kills it quicker.

jump the cold start valve and runs then.....what is going on?.

Yeah, I wonder too.

I've done everything you've done. except the ECU test, which Nick's helping me out on.

If i throttle it either hesitates then throttles up and backfires or it bogs down to almost nothing. To give you an example I can't even get the thing up on ramps to do work under the car, it won't give any power.


I've been thinking about the CPR, too. sort of in relation to this. (Can't do the full pressure tests, as one of my hose is currently split).

The intake is getting hot (never did before running for 10 minutes) and the throttle plate is down slightly at idle (perhaps causimg me to hear the throaty sound of the idle motor brass pipe sucking air in?

EDIt, oo I was going to mention, the thing is idleing at about 900RPM regardless of engine temp :/


questions!
Barzo.

[Rich H]

Quote:(Can't do the full pressure tests, as one of my hose is currently split).

Which hose is split? Surely this will be leaking fuel?

Quote:the thing is idleing at about 900RPM regardless of engine temp :/

It's normal for engine temp to have no bearing on idle speed - this seems to be a 'fault' with the Idle speed ECU/Temp sensor. 900 RPM is a little high, but this is often due to badly set up throttle spool/throttle plate linkages.

If you have a loud sucking noise soming from the intake, that's because the engine is struggling to idle, this is unlikely to be the idle speed motor. How far down is the metering flap at idle? Might be running too lean, have you checked for vacuum leaks?

Has this problem just suddenly started happening?

Just some thoughts...

[steve.s]

hi richard

You have a good memory....yes i did first clean the cpr fully...no difference.

then bought a new one...fitted and no difference.

fitted new plugs etc. new sensors in y pipe (and new heating pipe in valley).

pushing down slightly on flap and car would run (have not tried this time!).

also blocked the air inlet etc, and adjusted the screws...and car ran ok!.

last time car started chugged a bit, and eventually carried on running.

then saturday would only run with the jumped cold start valve (which obviously pumps fuel in)

had injectors out and the spray pattern looks ok.

had new pump filters etc. i will get round to doing a pressure test.
i still supsect the fuel distributor having a stick plunger maybe...i've had it out and cleaned it with acetone.

[NickT]

Barson Wrote:

steve.s Wrote:Hi

just wandered what your fault is.

i too suspected the idle motor (and possibly still do).

i tried the 12v test.

with a jump battery the thing jumps one way or other with a clonk.

Martin tested my idle ecu and came back ok.

also, make sure the ground to it is ok, and the feed off the coil.

my car is now playing up again. struggles to start runs 30 seconds then dies.

throttle kills it quicker.

jump the cold start valve and runs then.....what is going on?.

Yeah, I wonder too.

I've done everything you've done. except the ECU test, which Nick's helping me out on.

If i throttle it either hesitates then throttles up and backfires or it bogs down to almost nothing. To give you an example I can't even get the thing up on ramps to do work under the car, it won't give any power.


I've been thinking about the CPR, too. sort of in relation to this. (Can't do the full pressure tests, as one of my hose is currently split).

The intake is getting hot (never did before running for 10 minutes) and the throttle plate is down slightly at idle (perhaps causimg me to hear the throaty sound of the idle motor brass pipe sucking air in?

EDIt, oo I was going to mention, the thing is idleing at about 900RPM regardless of engine temp :/


questions!
Barzo.

Most do idle at 900rpm regardless of temp which is why I put in an extra 10k resistor in series with the thermistor.

NickT

[Barson]

RichH Wrote:

Quote:(Can't do the full pressure tests, as one of my hose is currently split).

Which hose is split? Surely this will be leaking fuel?

Quote:the thing is idling at about 900RPM regardless of engine temp :/

It's normal for engine temp to have no bearing on idle speed - this seems to be a 'fault' with the Idle speed ECU/Temp sensor. 900 RPM is a little high, but this is often due to badly set up throttle spool/throttle plate linkages.

If you have a loud sucking noise soming from the intake, that's because the engine is struggling to idle, this is unlikely to be the idle speed motor. How far down is the metering flap at idle? Might be running too lean, have you checked for vacuum leaks?

Has this problem just suddenly started happening?

Just some thoughts...

Yes, the hose does leak. My problems generally run concurrently
The hose split, but I cut the hose back and hammered on the bango fitting to repair is, but it still weeps fuel. It's the hose that goes from the top of the distributor to the CPR in.

The flap is maybe afew millimeters open, not much.

I have checked for leaks. nothing. I can reach (just about) the thermostat that opens and closes the vacuum (on the y pipe). the hoses are still attached.

Haven't adjusted the throttle spool. might give them ago later.

[steve.s]

hi

i would stop till you change that hose...a leaking banjo and the system under pressure.

if that goes and sprays petrol only takes a spark.

its amazing how difficult petrol is to put out. i burnt some old stuff i had in a can on the patio....wow!

how else do you get rid? our tip does not seem to take things unless it can be recyled into bog paper within the hour!.