Bronco won't Idle

[hangun61]

86 Bronco, full-size, 351, 4wd won't idle. It runs fine if the revs are kept up around 1200 but as soon as you let off the throttle, it sputters and dies.

I just changed the valve cover gaskets for leakage, and it ran fine before. I double and triple checked the routing of the plug wires and the I can hear the fuel pump run when the ignition is turned on.

Could this be a timing issue, or maybe a vacuum problem? Any help is greatly appreciated.

[taillight]

Look for a missing vacuum hose. Check everything you did.

[ibfishing]

[quote=hangun61]86 Bronco, full-size, 351, 4wd won't idle.

My jet sled has the same motor - and had the same problem. Darn near tore my hair out - and multiple pcv valves! I read something about the 351 being real sensitive to ignition cross coupling. So I dressed the wires so there was always a minimum of 1/4" space between them and even more when they crossed. That did it for me.

[wafrederick]

The 302 is the same way on the #8 cylinder with crossing the plugwire.It will eat up the piston.Another thing to check is the IAC motor which is also a common problem on Fords.Unbolt it with it plugged in and have someone turn the key on and off without the engine running.It should move with the key on and go back when the key is off.Try cleaning it first and replace it if this does not work.