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Discussion Starter #1
I have a 1995 3.9 that stalls when the car is revved sharply (even when stationary) or under braking or turning when coasting. I seem to replace the idle air control valve every couple of months which is bad enough but now it seems more abrupt than ever. I can start the car and let it idle without an issue for 20-30 minutes but if rev the car up to say 2,000 rpm and take my foot off the throttle it will stall. Just about everything on the ignition side has been replaced over the last 6 months.

Ironically, outside of the fact that it stalls at every junction it pulls better than it ever has.
 

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When you replace the idle air control valve do you set it to max open with a diagnostic tool of some sort?

Also have you looked at base idle and timing?


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No. I replace the sensor as described in the manual and then leave the car to sort out the settings. It can run like a pig for a day or two but will then generally run fine for a few months.

The idle and timing are good, this last time we plug the car into a Snap-On diagnostic computer and we checked everything we could and all seemed ok. Now it will start fine and will idle from cold but as soon as i reach a junction or even take the car over 2,000 rpm whilst stationary and take my foot off the throttle it will die. Occasionally it will try to raise the rpm but even then it is like the message is reaching the idle air control valve too late.

The TPS is about the only thing that i have not replaced over time. I am tempted to fit yet another control valve though this time it dies instantly as opposed to staggering a little.
 

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If you don't have a rovergauge cable I'd certainly buy one, program is free and at least you can see what the sensors are telling the ECU. Cheaper than a used TPS or any budget IAC valve.

The fact it does it both moving and stationary tends to rule out the speed sensor, but air leaks, maf, fuelling issues are all candidates. Rovergauge will save you much time and agro as you can discount fuel and coolant temps sensors, lamda probes.

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Show us your codes!

Often times people will replace their stepper motor when they get a Code 48 (me included), only for it to be something entirely different. Out of curiosity, have you replaced the stepper motor housing gasket as well? (photo below, ERR2926)
281578


However based on the symptoms, it could be a vacuum leak or air supply issue.
I'd recommend replacing your vacuum lines first, since it's cheap and will only do you good.
If it isn't a vacuum loss, the intake butterfly valve could be closing too much at idle (which could also throw a Code 48). Check and adjust the base idle, instructions below:
 

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Discussion Starter #7
I have the Hawkeye system which i use with the car. There is not an error code, the simply dies as soon as I lift off coming to a junction or turning.

I have replaced the speed sensor previously so I have a good understanding of those issues. The entire ignition system is new as was the Air Mass Sensor.

Occasionally the car would through up a lambda sensor issue with the B bank, never the other bank. This would only ever happen in traffic and after around 30 or more minutes of driving. The car has on one occasion shown an error for fuel pressure but after resetting the ECU it has never done it again.

I think I have seen a video of the Rovergauge on a Discovery that was used to calibrate the Idle Air Control Valve. I will look for the lead or instructions to make a lead.
 

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Show us your codes!

Often times people will replace their stepper motor when they get a Code 48 (me included), only for it to be something entirely different. Out of curiosity, have you replaced the stepper motor housing gasket as well? (photo below, ERR2926)
View attachment 281578

However based on the symptoms, it could be a vacuum leak or air supply issue.
I'd recommend replacing your vacuum lines first, since it's cheap and will only do you good.
If it isn't a vacuum loss, the intake butterfly valve could be closing too much at idle (which could also throw a Code 48). Check and adjust the base idle, instructions below:
All the vacuum lines are new. I replace the gasket each time a new stepper motor is fitted. I have given up on the cheap stepper motors, they either snap whilst being torqued or simply do not work.
 

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All the vacuum lines are new. I replace the gasket each time a new stepper motor is fitted. I have given up on the cheap stepper motors, they either snap whilst being torqued or simply do not work.
That's unfortunate to hear.
Are you replacing the stepper motor because it stops working, or do you replace it when the engine starts running poorly?
Is there anything physically wrong with the old stepper motors when you replace them?
 

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I have the Hawkeye system which i use with the car. There is not an error code, the simply dies as soon as I lift off coming to a junction or turning.

I have replaced the speed sensor previously so I have a good understanding of those issues. The entire ignition system is new as was the Air Mass Sensor.

Occasionally the car would through up a lambda sensor issue with the B bank, never the other bank. This would only ever happen in traffic and after around 30 or more minutes of driving. The car has on one occasion shown an error for fuel pressure but after resetting the ECU it has never done it again.

I think I have seen a video of the Rovergauge on a Discovery that was used to calibrate the Idle Air Control Valve. I will look for the lead or instructions to make a lead.
So your Hawkeye dosnt work is what your saying....
I have always used the onboard diagnostic code reader
That comes with a Range Rover classic..does work....
Also roverguage is a useful toy to play with....you might have better luck finding someone who can fix it for you
 

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I think I'd be inclined to suspect the throttle position sensor TPS as you've said back there in an earlier post.

If you blip the throttle quickly it will run lean (during that acceleration phase) unless the TPS recognises the rate of change in the throttle plate, that should supplement the fuel map with a temporary rich addition to make it go.

If it goes lean there and you close the throttle plate then the IACV has no facility to add fuel, it just modulates air against a fixed mixture point on fuel map. In essence the IACV just changes the air component to alter mixture and cause it to change speed as far as I can see.

As you've been through the ignition and you feel that the IACV is reacting but not quick enough, it could be the fuel component that's being misdirected from TPS report to ecu.
 
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