Thesnowman

My 88 951 idle fluctuates only on cold start. Once warm it's perfect! Have set TPS and idle.

Any things to look at first? ICV? If I pull that out (manifold off) I will want to replace it with a known working one or brand new. 951 parts are not cheap or easily avail when I am so don't want to just start swapping parts!

jerome951

To test the ICV, clamp off the hose from it into the intake while cold idling. See if the idle stops fluctuating.

Laust Pedersen

Maybe an old plasticized O-ring providing occasional sealing between the throttle body and intake manifold.
https://rennlist.com/forums/944-turb...-idle-2-a.html

Laust

Spidey944

yup sounds like a vacuum leak, clearances change when warm due to component expansion

Thesnowman

Thanks guys, will clamp the ICV and pull off the TB next week

Thesnowman

What makes me think it isnt a vac leak is the almost perfect idle when not on cold start map. Ive had cars with vac leaks and the fluctuation is there all the time

DirkSx1

I also had a similar problem. It turned out to be the temperature sensor. the one at the front of the head. I was give erratic readings until the engine got warm.

Thesnowman

This one? DME sensor? Will try unplugging it on cold start, did you test yours or just replace? Will test mine when my PS lines are fixed and back on the car.

fejjj

Yep DME temp sensor AKA Coolant temperature sensor.

I would just replace it for $20 from your local parts store.

Thesnowman

Ordered the dme sensor anyway as its on $35 nzd, will change that anyway. Can't hurt and it a week wait for the part anyway

Thesnowman

Changed the DME temp sensor today, looked a bit poked!

Will test it later this week after radiator and power steering lines go back in.

Thesnowman

Still does it, next to test the ICV by clamping it on next cold start (lines gone quite hard)