Random idle

[Brighouse-gti]

I've got this issue where the car keeps randomly idling. It doesn't matter weather the car is cold or at running temp, or if its wet or dry. Every now and then when the car is idling, like at the traffic lights for example, the rpm rises to around 2 to 2 1/2 thou, sits there for 10-20 seconds then drops back down to normal! It's as random as it gets, some days it does it others it doesn't? Its doin my head in!... especially at the traffic lights as the local boy racers keep thinking we're goin for the quater mile drag!! Any ideas?!

[gazareth]

could be the idle valve getting hot from engine heat and sticking randomly.

[Skywalker80]

Try and get hold of a decent isv to try. I thought mine was fine as it buzzed with the ignition on, but sometimes the needle would drop below the set idle then bounce up. I recently swapped mine for one a mate sold me, has made a massive difference to the idle and how the revs drop.

I was convinced mine was fine as most people say the buzzing noise indicates it's working. My old one might just need cleaning out.

[oakgreener]

Check the throttle body switches and the wiring for breakages. Blue temperature sensor is also a possibility.
I had a similar problem that I couldn't nail until I adjusted the tick over back to 800rpm and it's a lot better. Not perfect but a lot better than it was.

[jezza16v]

We had this on our 8v, it was dodgy connector on the blue temp sender, the outer plastic sheath to the wire looked ok but the wire inside was snapped just making intermittent contact.

[Brighouse-gti]

Thanks for the suggestions, I've got the day off work tomorrow so will have tinker, see what I can find!

[h8v]

The two cables going to the Idle Stabiliser Valve can break and give an intermittent connection; thus upsetting the idle.

The wires are bent through 180 degrees before they plug into the ISV.  The constant rocking of the engine causes them to flex and eventually break; usually where they bend.

Same thing can occur with all the other sensor and switch cables connected to the engine.

[Brighouse-gti]

Well I've given the ISV a good clean so will see if it improves things. If not it will be my next point of call. As always thanks for the suggestions! Will post back in a week of so let you know if its cured!