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'97 2.0 LPT
Every now & again after doing a few miles and pulling up at traffic lights the engine idle speed hangs around 1500 rpm and slowly falls back to 900. This is accompanied by Check Engine message which stays on for a few journeys. The erratic idle only lasts for a few hours and the message disappears after a day or so. Then all is fine until the next incident maybe a few weeks later.

I have checked for loose hoses etc around the induction...but can find nothing obvious.

I see in the Haynes Manual there is mention of an idle speed control valve....has anyone experienced propblems with this device and could it explain these symptoms ?
Thanks
Paul R
 

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your problem may be the idle valve on your car its located under the inlet manifold,you could try removing the electric connection to the valve (while engine running) then reconecting it, this can somtimes reset the valve, or you may have to remove it and clean it out with carb cleaner, as they are prone to cloging up with carbon deposits

another cause could be the throttle protenometer(probibly not spelled correctly) this tells the ecu of the throttle position and these can give problems by keeping the idle speed high, can be checked with a multimeter,
 

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I agree with AYM's suggestions:
The Haynes manual gives a good description of testing the 'Throttle Position Switch' (i.e. Potentiometer as referenced). Simple job with an Ohmeter to check if the 'closed' throttle position is being detected properly. If not, the unit needs loosening, slight rotation and re-tightening.

The Idle Control Valve (ICV) is a metal cyclinder with an air duct on one end and another protruding from it's side - at top of engine behind inlet manifold. They do clog up with engine breather oil over time and give the exact syptoms described - causing ECU 'Check Engine' message to flash up. The ICV may also be faulty - but check and clean first.
 

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I'd clean the idle control valve first before mucking around with the throttle potentiometer. Earlier cars had a throttle position switch which only detects 3 states - throttle closed, throttle open , throttle fully open and is fairly easy to set up. Trionic sytems, which Paul Rivned's is, use a poteniometer and I'm not too sure if the Haynes manual covers that but I think it's more difficult to set up.
 
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