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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
Idle Air Control Valve
Had mine out today but only had a few mins spare. Investigating high idle speed from cold, idling at around 1800rpm.

It wasn't really sooted up but a bit black on the tip. Cleaned that off with some brake cleaner and noticed the pointed tip has a bit of surface rust on it although I don't think that will effect how it operates?

Just wondering, should the spring bit push in? Mine spins but doesn't seem to push in?

Pictures are off internet





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Post #950378 24th Apr 2022 8:38pm
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mikeh501



Member Since: 07 Jan 2013
Location: United Kingdom
Posts: 1096

United Kingdom 
Ive got it in my head its a stepper motor so it needs a PWM feed to set its position when the engine is running. i.e. i dont think its sprung.
Post #950444 25th Apr 2022 11:11am
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Linds Hanson



Member Since: 16 Jan 2021
Location: Cornwall
Posts: 170

United Kingdom 
Yes its motor driven so winds in and out electrically. They are problamatic so its probably not functioning. If the battery has gone flat at any time the base idle setting may need to be redone
Post #950450 25th Apr 2022 11:31am
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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
Yes @mikeh501, I think they're also referred to as a stepper motor.

A bit more research and looks like they're threaded for the movement to take place, so a number of 'steps' between settings.

@Linds Hanson, I'm not sure if the battery has ever gone flat as I've only owned the 90 for 10 days. It does have a battery isolator on it which is always turned off after use so could that be having a negative effect on it?
Post #950517 25th Apr 2022 7:36pm
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Devon-Rover



Member Since: 22 Jan 2015
Location: South Devon
Posts: 824

United Kingdom 2014 Defender 110 Puma 2.2 USW Aintree Green
With it plugged in you can cycle the ignition and see it move.

Before blaming it go through all the rest of the system for vacuum leaks. Throttle butterfly spindle, plenum to the intake seal and the little pipe to the fuel pressure do hicky to name a few.

I had one that was misbehaving and the ignition timing was well out. Resetting it made a lot of difference. Also can be found on Fb, Ytube, Insta & Twitter @4WDSouthwest
Post #950521 25th Apr 2022 8:03pm
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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
Yep, they seem a bit troublesome from what I've read. It wasn't really grubby which seems to be the main tell tale. Whether flushing it with WD40 will help if it has seized, but cycling it as you say would show any movement to rule that in or out.

I've had a look at the butterfly spindle and all is squeaky clean in there and fully closed. Took off the TPS and had a quick look. Plenum chamber seems clean inside but gave it a quick clean anyhow.

Tried a bit of brake cleaner on a few of the vacuum pipes and when I did one pipe the revs seemed to drop so ordered that one that goes from the brake servo. Since ordering I've tried the brake cleaner trick again and it makes no difference on that hose. I was thinking of replacing all the hoses one by one before trying an new IAC valve.

Hadn't thought of the timing. It's got an ECU from RPi Engineering.
Post #950531 25th Apr 2022 8:30pm
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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
Fast forward to £11.95 for a new IAC Valve. Fitted it, started her up, cured, a lovely idle of around 850 - 950 rpm. Turned her off, started up again and back up to around 1700rpm. Been the same every time since then.
Bought a little circuit tester as couldn't find my old one. Out of the 4 pins coming to the valve, I'm only getting a reading from 2. Nothing from the other 2 so guess that could be the problem?
Post #951213 1st May 2022 2:08pm
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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
Fast forward a bit more and I've got it running at correct idle. Disconnected battery which I think has reset the ECU and she ticks over nicely.
New problem is that she now cuts the power at 3000rpm? Engine keeps running but pedal is dead. Leave it a couple of seconds and no problem until you hit 3k again.
She'll rev very freely sitting still in neutral up to 4 or 5k. Any ideas??
Post #952520 14th May 2022 2:15pm
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MercianRover



Member Since: 07 Apr 2022
Location: Midlands
Posts: 25

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
Throttle position sensor is faulty?

Do you have the use of a multimeter?
The Land-Rover 14CUV diagnostic manual is the most logical way to proceed with diagnosing the root cause of faults.

Related to the idle air valve I had a lot of trouble with blue box replacements failing after about 100 or so miles. Not sure where my present one was sourced from but may have had a green box.


Last edited by MercianRover on 20th May 2022 1:27pm. Edited 1 time in total
Post #953036 20th May 2022 1:23pm
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MercianRover



Member Since: 07 Apr 2022
Location: Midlands
Posts: 25

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
Van Diesel wrote:
Fast forward to £11.95 for a new IAC Valve. Fitted it, started her up, cured, a lovely idle of around 850 - 950 rpm. Turned her off, started up again and back up to around 1700rpm. Been the same every time since then.
Bought a little circuit tester as couldn't find my old one. Out of the 4 pins coming to the valve, I'm only getting a reading from 2. Nothing from the other 2 so guess that could be the problem?


The idle air valve is a stepper motor and the ECU drives the two coils inside it sequentially to step the shaft / cone in or out as required. You should measure resistance across pairs of pins, if only one pair has resistance then the other winding has failed and that motor is now an ornament.
Post #953037 20th May 2022 1:26pm
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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
The more I think about it the more I'm wondering if its the TPS?
I've spoken to RPi engineering a couple of times and they've said it could be MAF sensor or TPS but they'd need to plug in to ECU to properly diagnose now.
Post #953504 24th May 2022 6:09pm
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MercianRover



Member Since: 07 Apr 2022
Location: Midlands
Posts: 25

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
I'd disagree, follow the factory diagnostics process which I think only needed a multimeter and is arranged by symptom - check.

PM me if I've not shared a link within a week.
Post #953536 25th May 2022 8:34am
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MercianRover



Member Since: 07 Apr 2022
Location: Midlands
Posts: 25

United Kingdom 1998 Defender 110 300 Tdi CSW Java Black
Post #953538 25th May 2022 8:47am
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Van Diesel



Member Since: 12 Oct 2013
Location: Suffolk
Posts: 83

United Kingdom 1986 Defender 90 V8 Petrol PU Auto Shire Blue
Thanks for that Mercian, I'll take a look.
Post #953608 25th May 2022 8:58pm
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