Can't seem to sort out idleing speed-its too high?!

[RubySport]

My Renault clio 1994 1.4cc idles at around 1500 when in neutral. It has been known to drop to around 1100 once or twice but is mostly very high. We have replaced the idle control valve but it hasn't made any difference. The car has only done 26,000 miles and is in good nick.
Any ideas what the problem could be?

[Defcon5]

A temperature sensor of some sort? Vacuum leak?

Are there any other symptoms?

[RubySport]

No other symptoms, we thought that seen as though it has gone down to 1100 occasionally then it would be unlikely to be an air leak because that wouldn't self correct. Would an electrical fault be possible? Thanks

[nigel_bytes]

First check the coolant temperature sensor - if it's failed the computer will assume an average value to get the engine started and keep it running, but you'll have a high idle speed. To check quickly, disconnect the sensor plug with the engine idling - if it's working the idle speed will change, if it doesn't change, the sensor is suspect. Other possibility; Check the valve that controls the idle speed - they can get gummed up and stick.

[AceOfHearts]

Would an old Clio like this not have a carburettor?

[ian_uk1975]

I think this engine was available in both carb and EFI versions? If it's carb, I'd check the automatic choke. Also worth checking the throttle cable and lubricating it regardless of whether it's EFI or carb.

[maniac0796]

Revs can only be increased by letting more metered air into the engine. So think about it logically. What you have to decide is if it's cause or effect?

Now I assume being an old clio it's single point injection?

[RubySport]

Yes its a single point fuel injection. We will check the coolant temp sensor in the way you described and see if that works, thanks.

[maniac0796]

I can't tell you specifics about this system without a wiring diagram, but as I said above, the only thing that can control revs is letting metered air in.

So either:

Your throttle is stuck open (build up of gunk or badly adjusted cable)

Your idle control valve or motor has jammed up. Something like this might have an acuator that directly controls the butterfly valve for cold starting as well as an idle control valve. For instance, K11 Nissan Micra's have a coolant controlled waxstat which actuates directly on the throttle cam, as well as an ICV.

Something which controls the idle control valve is playing up (temperature sensor, power steering load sensor, air con switch, some alternators can have control of engine revs etc etc.)

[RubySport]

Coolant temp sensor seems to be working ok, we disconnected and reconnected it and it affected the revs. The car has a brand new idle control valve we bought in the last few weeks but today we read that it needs to be reset once it has been fitted so followed the resetting procedure as described in the haynes manual using a 5mm shim. Now the car won't idle at all and wants to cut out altogether unless the accelerator is pressed so we are now in an even worse situation! Could it be the rev counter itself is giving the wrong reading? Or could it be that the engine needs revs of 1500 in order for it to work? Any ideas greatly appreciated.

[maniac0796]

But does it have some sort of automatic choke as well as the idle control valve?