-1987 GT, 5spd

Scenario:
*On cold mornings only* i start the car up it idles high for a few seconds, then the idle drops and drops and drops till the car shuts off, if i give it gas it stays alive. Only happens on the first startup on cold mornings, once the car has rolled for about a minute its fine. Wednesday it died on me twice in my laneway.

Anyone with any feedback/reason?

Thanks
Marc L.

 

Is the Engine/fuel system completly stock?
Mods?

 

Sounds like a dirty IAC valve, it's the cylindrical thing on the side of the throttle body with two 8mm bolts holding it on. Remove it, spray inside it thoroughly with throttle body cleaner and shake it and anything else you can to try and clean it out. Keep doing it til the inside is shiny and most, if not all, carbon deposits are gone.
It could also be a few other things, but this is the most common problem with our cars. Other sensors such as the coolant temp sensor on the passenger side on the coolant bypass lines can become faulty and cause hard cold starting. Try cleaning the IAC and let us know what happens.
SS

 

Engines mods are pretty basic (Bigger TB, Upper/lower intake, CIA, Phenolic spacer), the IAC motor I cleaned out before storage, I have a new coolant temp sensor i've been meaning to put in, hopefully that will fix it. Thanks guys

 

are there any mustangs that use idle speed control as opposed to IAC?

 

is this the surging idle? bounces from 1200 - 400 rpms?
look up surging idle checklist.

 

Are you also running the factory EEC with or without a tune?

 

sounds like a simple vac leak.check all your vac lines for small cracks it does not take much

 

Agreed I had this exact same problem once,... broken vacuun line at upper intake.

 

Yup factory Speed Density "Computer" no tune as they are not tunable.