Megane IAC valve

Symptoms are over-revving, idling fast, revs going up and down on their own etc. etc. I told the owner to remove the IAC valve and he said it was very
dirty, as is the orifice wot it came out of.
Should the plunger move in and out when pressed manually or is it just when the motor (presumably?) operates it? There doesn't appear to be any movement visible when the ignition is turned on and the valve is out of the car.
The car idles at ~2000 rpm and it makes no difference to the running at all if the valve is connected or not.
If he gets a new valve is the air passage likely to be bunged up enough to prevent it doing its job? If so, how big/long is the air passage?
Si
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Mungo "Two Sheds" Toadfoot wrote:

sounds more like an air leak (likely) or the throttle valve itself is bunged up and held open by crud (less likely)
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Mrcheerful wrote:

Noted, thanks.
Si
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Mrcheerful wrote:

He's checked what he can see and found nothing wrong. It has a new IAC valve now but ran the same after fitting it. After spraying loads of WD40 into the IACV hole, and much cleaning, it started and ran normally for a 5 minute run. When, on the phone, he started it again to demonstrate his genius to me it revved itself up to ~4000rpm so he quickly turned it off and tried it again. By ged it did rev itself up! He gave the accelerator a swift kick to see if it would settle down but it made no difference and he had to turn it off again.
What's got the capability to do this? Surely it can't be any of the temp sensors? It's not just hunting or dipping down and then over-compensating for a potential stall, it's really going for it!
Si
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Mungo "Two Sheds" Toadfoot wrote:

find out where the air is getting to make it run that fast is the answer. he needs to check the throttle valve actually closes and that no air is leaking in at manifold gaskets/split pipes etc. spraying around some flammable gas with the engine running will quickly show any suction leaks.
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Mrcheerful wrote:

What ho! I'm back from my venture to see to the shit French car. I found no air leaks after checking the manifold and every connection and pipe I could see.
I took out the new IAC valve to have a look at it and while it was out I got matey to turn the ign on and off a few times. All it did was twitch *very* slightly. What are they supposed to do? The plunger goes in and out manually as you'd expect so I gently pulled it right out and put it into its hole so that the plunger was seated properly when pushed back in. It ran fine then and idled nicely, where before it was idling at ~2000rpm. After a dozen or so practise starts it was still behaving itself but when it was taken out for a run, after I'd gone of course, it went back to buggering about again.
I'm assuming the IAC valve isn't working as it should and is letting too much air through, but why?
Si
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Mungo "Two Sheds" Toadfoot wrote:

Did you actually spray around some flammable stuff to check for air leaks, because a visual is not enough.
without it running it the iacv only twitch a bit, that is normal. if the engine thinks it is running too slowly then it will open the valve to increase speed, there are many inputs that have to be right for it to operate correctly, including but not limited to speed sensor, crank sensor, temp. senders etc. etc.
finding someone that knows the car type (and likes them !) will probably be the most cost effective way forward.
a quick search for 'megane high idle' shows that it is a common fault.
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Mrcheerful wrote:

No. I intended to but the engine is set so close to the back of the bay that there's nothing to see and no room for the can I had with me. I also intended to check the inlet manifold but could reach just one bolt.

Crank sensor. Hmmm... I noticed that the two 10mm bolts holding the bit of ironmongery on which the crank sensor is mounted are rounded off. Someone's been playing. Also I noticed that where the sensor enters the housing there's a gap all around it and the ring gear is clearly visible. That can't be good, surely?

Indeed it is. Hateful things. I'll try to find a wierdo who likes them.
Ta muchly for your help.
Si
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Mungo "Two Sheds" Toadfoot wrote:
Oh, and the plugs were black and sooty.
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Mungo "Two Sheds" Toadfoot wrote:

that could point to the ecu thinking it is colder than it really is. an expert will plug in and make sure that the sensor readings coming back are within spec. however, since there have been previous attempts on it then I wouldn't hold my breath, just advise him to out it and move on.
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On Thu, 10 Dec 2009 17:33:21 -0000, Mungo \"Two Sheds\" Toadfoot wrote:

WD40 is the wrong stuff to use. It's nice and slippery when wet but it dries waxy. It's a water disperser, not a lubricant.
Use some carb cleaner to clean it and then spray lightly with a light oil, 3in1 should be ok.
--
Regards - Rodney Pont
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rp wrote:

Okies, ta. I'm going to look at the bloody thing myself on Sunday before he sets fire to it. I hate French cars.
Si
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