double idle speed when cold

[kabaman]

A problem I've been having for a while now is that from cold the car idles at double it's correct RPM.

Once it's warm I can turn it off and back on and it idles fine.

I've changed a number fo things so I haven't got a clear idea of which one specifically might have caused this(ECU, fitted MSD, replcaed idle speed motor/valve (with a cheap one)).

It's odd that it is double speed and it's odd that it sorts itself out when it's warmer.

Has anyone else ever had this problem?

Thanks,

Neil

[SonicHedgeHog]

What is the standard hot and cold idle speed?

[kabaman]

err...

Warm is around 700rpm. Cold is around 1400rpm on my car at the moment.

Cheers,

N

[SonicHedgeHog]

kabaman said:

err...

Warm is around 700rpm. Cold is around 1400rpm on my car at the moment.

Cheers,

N

Interesting. Just got back from a long run and mine was idling at 1400rpm. Looking forward to educated replies to this question.

[Toffer]

If you drive of with the engine cold and do not stop until the engine is at operating temperature, the idle tick-over is faster than it should be (900 RPM). Pausing for a moment the idle kind of resets itself and is perfect from then on...

[kabaman]

I need to turn the engine off again and back on. The real pain is shuffling along in traffic with the car at 1500rpm for the first ten minutes arrggghhh

[Toffer]

kabaman said:

I need to turn the engine off again and back on. The real pain is shuffling along in traffic with the car at 1500rpm for the first ten minutes arrggghhh

If it is safe to do so, please stop next time this happens and wait for a few seconds and see if the idle settles down. If not, you may need to clean the idle stepper motor assembly (lots of threads on here).

[kabaman]

It never returns to sensible idling unless I kill power. Stepper motor has done about 300 miles since new.

Neil

[RichB]

Maybe but it still sounds like a stepper-motor issue. It is quite normal even when the engine is warm for the idle speed to run at say, 1,000 for 4-5 seconds before settling back down to 700.

[jimed]

What sort of stepper motor is it Neil - I understand there are some dodgy ones around which could possibly cause problems??
Jim

[blitzracing]

The cheap one I bought let air in past the motor,(via the rubber seal by the connector) so the ECU could never sort out the tickover out with this extra air getting in. The whole tickover and mixture control system is pretty finely ballanced and can lead to some idle funnies. You need to do a simple voltage test on each lambda probe output, and chech that both start switching between 0 and 1.2 volts (black to white wires) within about 20-30 seconds of starting, to show the ECU has set the fueling correctly as this is the point the RPM should stablise at around 7-800 rpm. If the probes are giving a constant 1 -1.2 volts its overfuelling, or if its 0 volts its lean, faulty probes, or a bad misfire. There are certain "fault" conditions that will cause the ECU to hold the idle high to preserve the catalysts, but I dont yet know what these are.