Celica 1.8 Idle Speed

[wolfitt11]

Can anyone offer any advice on the following.

My 1996 Celica ST 1.8 has a problem with the idling speed. Basically it won't come down to spec and sits at 1100 to 1200 rpm. The only time that its comes anywhere near to what it should be (850 rpm) is when it gets hot towards the red of the temp range. The fan kicks in and the idle hovers around 900 rpm. On normal driving it never comes down to below 1100 rpm. 

I have unplugged the temp sensor and the rpm reduces and have replaced that and its made no difference. Swapped over the idle control valve and that's made no difference and the valve is getting a water supply when the car warms up. Have swapped out the alternator and Battery out to.

It runs really well with no fluctuation on idle or reduced power.

Has anyone encountered this at all and can offer a possible cause and solution?

 

[alan333]

You mention that the temp gets towards the red.  This shouldn't happen - perhaps you have an overheating problem which also causes funky idling?

[wolfitt11]

Yes it does get hot when its been idling for about 10 mins. Fan kicks in and it brings the temp down along with the rpm. Run it normally and it runs absolutely fine but the idle speed never drops below 1100 rpm. Have also checked the cooling system rad off flushed and checked, hoses checked and tightened with a good system pressure and have even replaced the rad cap. Its not really indicative of a cylinder head leak as there are no signs in the oil or coolant loss et

[alan333]

It shouldn’t get really hot sitting idling. Is the rad hot?  Could it be a water pump problem?

[wolfitt11]

Yes the rad is hot and top and bottom hoses are pressurised. I did think it may be a water pump problem but the pressure and temperature are all ok in normal running. If the pump was an easy job to change I agree I would try that. My main issue really is the idling speed and the fact that It won't come down to anywhere near normal unless the fan is running. As I say there are no issues with the cars performance but there is something obviously wrong by the way it idles.

[wolfitt11]

Well a new Toyota Thermostat has been fitted and the idling speed problem is fixed. All back to spec and working ok. However,  the overheating problem looks like it was a problem with gauge as it now reads permanently in the red zone when it gets up to temperature. Any ideas?