I have a 84 Tbird with a 5.0L CFI engine. When starting the engine, the fast idle runs too fast - around 3500 rpm. And most of the time the fast idle varies from fast to way too fast. Also, the automatic fast idle kickdown doesn't work. I've narrowed down the problem to the control diaphragm that connects to the thermostat. Does anyone know of a parts source for a replacement pulldown control diaphragm for a CFI engine? Thanks!
If you can find a part number give these guys a call, they might have it: http://www.greensalescompany.com/
The fast idle cam has three steps. When vacuum is applied to the control diaphragm it should move the idle cam off the highest idle step to the middle step.
The thermostat, as it warms up, moves it the rest of the way until it drops off the fast idle cam.
Did you put a piece of hose on the vacuum nipple of the control diaphragm and suck on it? To see if the diaphragm is leaking?
I have been trying to remember if the pre-cat converter (pre 1975) carbs had the vacuum pull down (control diaphragm) on the fast idle cam.
I think they just had the electric choke (thermostat) to move it off fast idle. So, I think your thermostat should move it off fast idle even if the control diaphragm is not working. Just not as fast.
The thermostat is powered by the stator output on the alternator. It should be 7-8 volts with the engine running.
Do you still have the stock alternator?
pics