I have a 91 Bronco w/ 302 (EFI) and the truck is idling really strange lately. I should probably say upfront that I don't drive the truck much because I don't have my insurance yet, but I do take it out around the neighbourhood occasionally. Anyway, when I first start up the truck it goes up to between 1000 and 1500 RPM, but then almost immediately drops to around 400-500 RPM. After about 2 secs it jumps back up to between 1500-2000 RPM. This fluctuation usually continues, as it seems to rev up by itself between 1000 and 2000 RPM. Once the truck is warm, it settles around 700-800 RPM.

I don't really know whats going on. My air filter is clean and I just put in a new Fuel filter. My fuel pump does hum quite loudly but I checked the pressure and it reads around 45 PSI. Also when its reving quite high (around 2000 RPM while its idling/warming up,) I hear a faint clicking sound in the engine and then it will drop back to normal RPM, then increases up again and repeats until warm.) Not really sure where to go from here; I'm also getting a lot of water out the tailpipe? Think its probably just condensation from sitting and not driving a whole lot, but if anybody could help me with any of these problems that would be great! Thanks in advance!!!

 

I had a similiar problem with my '96. Picked up a can of air intake/ throttle body cleaner, not carb cleaner, spray down the throttle body. I took the idle air control (IAC) valve off the side of the throttle body and cleaned it as well. Sometimes the carbon build up will cause the valve to stick.
Also check the TPS, if this sensor is faulty it will give you idling problems. Hope this will help you out.

Warr

 

I will look into those things and go from there! Thanks alot!!