This is really a problem with my Aerostar, but I think the idle circut is very similar to the one in my '95 F-150. So I thought I might get a little more exposure on this board...My '93 areostar barely keeps itself running after a cold start. It will start up, rev up, and then almost die. It will repeat this reving up and down cycle until one of the following coditions exists: the engine warms up, the air conditioner is turned on, or the transmition is shifted to something other than park or neutral. Earlier replies to a similar post on this board mentioned the idle air control valve and/or the coolant temperature sensor. I think the IAC and the Temp. sensor are OK becuase it idles fine after the conditions are met. Any ideas??

 

Have you checked the Idle Bypass Valve ? It sounds like it needs to be cleaned . All the things you mentioned causes the engine idle speed to increase . It sounds like it has carbon blocking the passages when its in its idle position .

 

This may sound odd, but how is your alternator? My truck kept doing something similar and I noticed the alternator wasn't pushing enough juice, with any accessories on. So it would almost die off. Is this your problem I doubt, but in case the above response doesn't fix it then check this out. Yeah I know it sounds silly, but thats what fixed my truck.

 

Yes, I have cleaned the bypass valve. It didn't change anything. I mistakenly refered to this as the Idle Air Control in my original post. I compared this voltage to, and resistance of this valve to the one on my truck and the readings are similar.

 

You should also clean the throttle body bore and flapper. This seems to make the most difference on all my vehicles.
Phil