What is all that high idling speeds all about?

[groucho]

I was driving today in my 1998 Griff with the blower on to demist the windscreen. I parked up for a few minutes, leaving the blower still on. When I got back into the car, I noticed a strange buzzing sound, as it happens it was the blower, so I turned it off. On starting the car it idled at 2500 rpm for about 2 minutes and then returned to normal. I don't know whether I have a dodgy blower or not, but it works fine.
It seems with these cars that if there is anything out of the ordinary going on they always idle fast, as it happened before when I accidently armed the alarm from inside when I was just about to drive off and the alarm went off, then idled fast.

My question is does anyone know why they do this? as I have read threads before about this happening.

Grouch

[beano500]

May or may not be linked

A few seconds of logic.....

Idle speed is determined by ECU

ECU is fed by various bits of information

One of these will be water temperature

Perhaps you have an airlock in the system (possibly from slightly low coolant level)

Hence ECU is being fooled?



Well - that's my daft theory anyway!

[BogBeast]

"strange buzzing sound" maybe the stepper motor. Mine someimes grinds and buzzes on ignition on, causes flaky idle. On its way out I suspect.

[FlipFlopGriff]

Ours did that too when we bought it. Now put Redex in with every fill up and it doesn't now do it. Not sure if this is the only factor or whether it's due to the water temp not getting above about 75 degrees.
FFG