Megane IAC valve

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

Noted, thanks.

Si

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

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.

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.

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

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

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.

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

Oh, and the plugs were black and sooty.

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.