Unusual Revving At Idle

[macdonb2]

Hi my 2004 1 litre yaris has developed a problem where at idle she will start to higher and lower the revs by at least couple of hundred all by itself.This is a bit unnerving and I would appreciate any help.

Kind Rgards,

Brian.

[Madasafish]

Hi my 2004 1 litre yaris has developed a problem where at idle she will start to higher and lower the revs by at least couple of hundred all by itself.This is a bit unnerving and I would appreciate any help.

Kind Rgards,

Brian.

Is the engine cold or hot?

How many miles has it done?

Has the coolant and antifreeze been changed recently.

The Idle control stepper motor is driven by a waxstat and the tube can get blocked by dirt if the coolant is not clean.. BUT until we know more, ?

[macdonb2]

Thanks for your reply, it tends to do it after about 5-6 miles so when hot. She only has 24k on her and no the coolant hasn't been changed since new. The only thing is that if you turn the ignition off and restart her it seems to go if thats any help to you??

[andycam06]

i was going to say the idle control valve alright.

i had a similar problem with my diesel and it ended up being the fuel pump acting up due to dirty fuel, not saying that is your issue as petrol is usually very clean.