Fast idle?

[JohnG]

What controls the fast idle when the motor is cold? IAC or computer or other?

When starting up in the morning, the fast idle on my 86 2.9 is like 2000. Since it fires on the first hit I really hate running it that fast while cold.
Thanks!

 

[ericbphoto]

What controls the fast idle when the motor is cold? IAC or computer or other?

Both. The computer controls the IAC to control idle speed.

Could be a vacuum leak.

Does it do this every time you start? Or only on a cold start?

 

[JohnG]

Only cold starting.

 

[Bgunner]

High idle should be 1800-ish rpm when cold and then go down from there.

 

[JerrySab]

Does idle fall after a few minutes? or is it persistently high? Are there any other symptoms? Rough idle, stink or fuel smell or black exhaust?

Mine takes longer than I'd like to warm up, but gets there in 3-5 minutes. I blame the rad fan clutch - which isn't bad - that remains engaged until the silicon fluid loosens up. On cold start, with fan going full bore, cooling what the ECU is programmed to be warming, they kind of fight each other for a while.

If idle is just high with no other smells and doesn't settle into place after 3-5 minutes warm up time, it most likely vac leak.

 

[JohnG]

Yes, it settles down after a minute or two with no other symptoms. The issue happens only when cold. Starts on the first hit, it revs to 2000, when I put it in gear, it drops to like 500 and almost dies. After warm, all is well.

The IAC is not a Motorcraft so that might be part of the issue.

 

[JerrySab]

Yeah maybe? Mine does exact same nonsense. Near stall after first shift. Fine thereafter. I quit hunting that gremlin and just give gas pedal a little tap just before it chokes.