What should fast idle be?

[vrracing]

The hot idle is between 750 and 775. Cold ("fast") idle is just below 1000rpm and our morning lows are high 70's though the garage is probably warmer than that.

I've OCR'd the FSM and the S5 Service Highlights but my searches don't lead me to a number for the fast idle rpm.

Thx

[Pete_89T2]

Those RPM figures sound about normal for the temps you stated. On a colder day, say < 45F, you could expect a higher idle when you startup, about 1200~1500 RPM.

It's been a while since I looked thru that part of the FSM, but I think the reason no fast idle RPM is listed is because the adjustment procedure is done with the car shut off & cold. The FSM has you adjust the fast idle cam with the engine cold (about 70F, IIRC), and you tweak the adjustment screw so the index marks on the cam line up per the FSM picture.

With the engine cold, the thermowax plunger that the fast idle cam rides on is fully retracted, and as the engine warms up and hot coolant flows thru the thermowax, its plunger extends and gradually releases the fast idle cam.

[vrracing]

Yeah, we followed that procedure and used a piece of appropriate thickness wire to set the butterfly valve. But it turned out the BAC was leaking and our cold idle was at 1800 and hot idle around 1100. So we put our PVC TMIC on and manually adjusted the hot idle.

Since we are in the ballpark we will just run it as is. Next time we have the tb out we'll recalibrate it. We will see when we get cold in the winter.