Idle speed control
Discussion
Right, on the 2.9 the idle speed control valve is on the front of the plenum chamber (just in front of where the two air hoses take air into the engine). You can see it in the bottom centre of this photo (click to make it bigger):
It's effectively an electric air bleed, controlled by the ecu to let in just enough air to keep the idle speed right. They can soot up though, or fail altogether.
To clean it, disconnect the electrical connector, then unbolt two 10mm bolts that hold it on. You can clean out the valve and the drillings in the throttle body with carb cleaner. To clean it more thoroughly, remove the two screws and split the solenoid from the valave, and clean it out (using a finger to hold the valve open).
It's effectively an electric air bleed, controlled by the ecu to let in just enough air to keep the idle speed right. They can soot up though, or fail altogether.
To clean it, disconnect the electrical connector, then unbolt two 10mm bolts that hold it on. You can clean out the valve and the drillings in the throttle body with carb cleaner. To clean it more thoroughly, remove the two screws and split the solenoid from the valave, and clean it out (using a finger to hold the valve open).
Steve
When you take off the idle speed control valve you might want to check the condition of the gasket (where it joins the front of the plenum chamber). I took mine off to clean and discovered the gasket had split - this can have the effect of letting air in. They're only about 50p to replace.
Cheers
Jaye
When you take off the idle speed control valve you might want to check the condition of the gasket (where it joins the front of the plenum chamber). I took mine off to clean and discovered the gasket had split - this can have the effect of letting air in. They're only about 50p to replace.
Cheers
Jaye
Jaye R said:
Steve
When you take off the idle speed control valve you might want to check the condition of the gasket (where it joins the front of the plenum chamber). I took mine off to clean and discovered the gasket had split - this can have the effect of letting air in. They're only about 50p to replace.
Cheers
Jaye
Good point.When you take off the idle speed control valve you might want to check the condition of the gasket (where it joins the front of the plenum chamber). I took mine off to clean and discovered the gasket had split - this can have the effect of letting air in. They're only about 50p to replace.
Cheers
Jaye
I made a gasket out of a business card and some vaseline...
mep12345 said:
Barkychoc said:
tvrgit said:
Good point.
I made a gasket out of a business card and some vaseline...
I've used a corn flakes packet in the pastI made a gasket out of a business card and some vaseline...
Maybe that's what TVR used anyway
No, seriously, it helps prevent the cardboard sticking to the castings when you take it apart again... that's my excuse and I'm sticking to it (or not, as the case may be)
)thanks for all the tips,got the car running again,cleaned the (thing ) as told ,still find the revs ideal fast and not responsive to go back to tick over.what should they tick over on ,mines 1000 rpm,although when we disconnect the sensor it drops down to tick over more easerly seems more responsive and ticks over around 800 rpm
steve wilton AM said:
thanks for all the tips,got the car running again,cleaned the (thing ) as told ,still find the revs ideal fast and not responsive to go back to tick over.what should they tick over on ,mines 1000 rpm,although when we disconnect the sensor it drops down to tick over more easerly seems more responsive and ticks over around 800 rpm
Right now try this. Start it, rev it a little to get the ignition light off then leave it to idle until it heats up and the fan cuts in then goes off again. Then see what it idles like.It works on mine. Don't ask me why, just try it!
If that doean't work then you need to look elsewhere.
Disconnecting the ISCV only puts it into "limp home" or "faultfinding" mode, and removes all the mapping etc. That doesn't mean that's where the fault is, it just means it over-rides many of the sensors.
tvrgit said:
Disconnecting the ISCV only puts it into "limp home" or "faultfinding" mode, and removes all the mapping etc. That doesn't mean that's where the fault is, it just means it over-rides many of the sensors.
I'm not sure this works on the S3. Well it certainly doesn't work on mine and the ignition still appears to be under ECU control because the timing flicks all over the place. When I place mine in service mode the timing is rock solid. However there are so may people and dealers who say disconnect the ISCV that there must be something in it. Maybe it only works on CAT engines?
Getting back to the OP's issue. I'd recommend getting a Gunson/Draper tester and place the ECU in service mode. Then check/set the timing to the appropriate setting (depends on the ECU you have) and see how that goes. If the idle is still too high then you might need to adjust the throttle stop to close the butterfly.
Jed
Jed-S said:
tvrgit said:
Disconnecting the ISCV only puts it into "limp home" or "faultfinding" mode, and removes all the mapping etc. That doesn't mean that's where the fault is, it just means it over-rides many of the sensors.
I'm not sure this works on the S3. Well it certainly doesn't work on mine and the ignition still appears to be under ECU control because the timing flicks all over the place. When I place mine in service mode the timing is rock solid. However there are so may people and dealers who say disconnect the ISCV that there must be something in it. Maybe it only works on CAT engines?
Jed-S said:
Getting back to the OP's issue. I'd recommend getting a Gunson/Draper tester and place the ECU in service mode. Then check/set the timing to the appropriate setting (depends on the ECU you have) and see how that goes. If the idle is still too high then you might need to adjust the throttle stop to close the butterfly.
The throttle stop is supposed to be pre-set - if the idle speed subsequently changes so that it's too high, you have to find the cause. If you have an air leak for example,, closing the throttle butterfly won't make any difference - the air will still leak in, or the ISCV will open further (it bleeds air in past the butterfly to control the idle speed).If the idle speed is too high, either a sensor is broken (for example it thinks the engine is too cold so is over-fuelling) or there is an air leak on the engine side of the throttle butterfly - the inlet manifold, plenum, vacuum hoses, etc.
Can we have some clarification on this - from you guys who know 
What is the idle speed for a S3 (non cat) supposed to be?
Just for more background to the complex nature of the S3 - I disconnect my battery each time I put the car away (as tends to be unused 2 weeks at a time & the immobiliser/alarm runs the battery down) - this buggers up the ECU and hence the idle speed.
Giving the car a full blast (eg BNG at the weekend) gets the idle speed settled at 1000rpm.
Having already cleaned the ISCV, checked for air intake leaks, etc. is this OK (as all seems OK with the possible causes of any over rev on the idle speed) again
To put all our minds at rest can anyone give us a definative answer???
Ta very much.
Jaye
What is the idle speed for a S3 (non cat) supposed to be?
Just for more background to the complex nature of the S3 - I disconnect my battery each time I put the car away (as tends to be unused 2 weeks at a time & the immobiliser/alarm runs the battery down) - this buggers up the ECU and hence the idle speed.
Giving the car a full blast (eg BNG at the weekend) gets the idle speed settled at 1000rpm.
Having already cleaned the ISCV, checked for air intake leaks, etc. is this OK (as all seems OK with the possible causes of any over rev on the idle speed) again
To put all our minds at rest can anyone give us a definative answer???
Ta very much.
Jaye
Steve Heath's book says 2.9 non-cat v6 is 900rpm idle and for the cat fitted ones it is 1000rpm - I can confirm my S3c idles at 1000rpm. Re the disconnecting the battery; it is possible that the management system has to reset itself when the battery is reconnected and this could be part of the problem?? Others may know more about that than me though ....
Jim
Jim
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