I just bought an 1985 bronco 11, v6 2.6 engine 5 speed (or close to that engine size).
When you start up the truck, it will idle fast for a few seconds, then really slow down, idle fast again and slow down. This just keeps on going, fast then slow idle. Any suggestions.
Thanks Dave

 

My 1986 B2 does the same thing. The only thing I found that works is as soon as I start it, while it is idling fast put it in gear. Not sure why, but it runs fine from then on.

 

My '84 just started doing that. I was driving home last week and it started losing RPMs and almost cut out, I turned the fan to high and it smoothd out a little bit. I did a full tune-up and the problem didn't change, it only starts occasionally and has the erratic RPMs. So I decided to rebuild the carb, it started on the first try but was racing, I lowered the idle a bit and it went back to cycling. Not sure what to do. Was thinking the gas pump was starting to fade? I noticed the carb was dumping a lot of gas out the carb. ANy one have an idea?

 

if you have a v6 in 1985 on a b2 im gonna assume it is a 2.8L with a computer controlled carb. What you are describing is normal for that engine to an extent. Mine does and so do all the others like it i have heard. It is the computer which is rather slow constantly adjusting the idle at warmup. You are just experienceing a little bit of lag because its carborated and not fuel injected. To an extent i mean it should smooth out once it warms up and the cycling shouldnt be overly drastic. On mine it is noticable but not horrible. It couldnt hurt to check for vacuum leaks though. That could cause your problem. Take some carb cleaner and spray it around the carb base and sides, front and back of the intake manifold. If it suddenly smooths out while you are doing this you have a vacuum leak.

 

yeah mine does the fast and slow idle, and the guys at ford did a bunch of tests on it and found nothing wrong. they said that it acts like the choke on a carburetor. mines an efi.





86 b2 xlt 2.9 V6

 

 

My 85 Bronco II 2.8 V6 engine has a 20k ohm resister in a wire going from the coil back to the computer. The official wiring diagram from Ford does not show it. Ford could not find it in their parts computer. The 4 cylinder wiring diagram shows it. On mine, the idle was high most of the time. I found that the resister was open. I made my own with a part from a 20k ohm resister and it fixed the fast idle and idled normally whether cold or hot.

 

For the EFI models FORD makes an adjustable Idle Air Kit which normally solves this problem as long as the TPS is working properly. Part# F2PZ-9F939-A.