Low Idle Speed When Cold, High When Hot

[acox99 74 1 Cars]

In the mornings when i first start the car, it will take a while until it will idle, and constantly stall, as it warms up the idle speed increases, and when hot it will idle at 1200-1400rpm, what could cause this, many thanks

[Pugwebgeek 0]

My first guess is that the Throttle Position Switch (TPS), Supplementary Air Device (SAD) or Engine Temp Sensor isn't working properly.

How long has it been like this? Have you had to increase the idle to avoid it stalling when cold? If so, that explains the high revs when warm

 

When you first start the car, does it really struggle or is it only after 30 seconds? Reason for asking is because the ECU increases the enrichment for the first 30 seconds.

 

The TPS should close the contact between 2 & 18 when your foot is off the accelerator. It's easy to check if you have a voltmeter etc

To check the SAD, start the car from cold and pinch the hose the comes off the massive rubber elbow that runs from the Air Flow Meter to the Throttle Body. If the revs drop it's working, if they don't then it isn't or there is an air leak somewhere

The ETS is harder to check but if you check the resistance across its 2 terminals it should be about 2000-4000 ohms depending on the temperature of the engine.

 

I'd try those first

 

Colin