Extremely high idle

[Sludawg40]

Hey all,
I just recently made this account after buying a 1989 Ford bronco II recently, when I got it ran like a dream, but after replacing the valve cover gaskets to stop an oil leak my bronco II wouldn’t start. Quick trip to Walmart for a damn battery got it to start... but to my surprise as soon as I start the car it almost redlines at 5k on the tach and sounds just like an airplane going supersonic... I’ve replaced the vacuum lines as they were all brittle don’t know if they’re on there 100% right but there’s no openings on the intake leaking air in either... any help would be deeply appreciated thank you so much

 

[Curious Hound]

Sounds like your throttle is stuck open or you have a major vacuum leak or your idle air control valve (IAC) fell off. Check again for leaks, electrical connectors pulled loose or something wedged in the throttle linkage.

 

[Sludawg40]

Sounds like your throttle is stuck open or you have a major vacuum leak or your idle air control valve (IAC) fell off. Check again for leaks, electrical connectors pulled loose or something wedged in the throttle linkage.

Hey I just got back inside from checking all the electrical connections, those seemed in order, as well as the vacuum lines, as for the throttle body it remains closed the whole time, so I guess it off to pick up an IAC Valce? And see how that goes.

 

[Curious Hound]

Hey I just got back inside from checking all the electrical connections, those seemed in order, as well as the vacuum lines, as for the throttle body it remains closed the whole time, so I guess it off to pick up an IAC Valce? And see how that goes.

I don't know if that can send the idle as high as you're describing. With the engine running, unplug the IAC electrical connector. The engine should stall as the valve closes.

 

[Sludawg40]

I don't know if that can send the idle as high as you're describing. With the engine running, unplug the IAC electrical connector. The engine should stall as the valve closes.

Unplugged the IAC with the engine running and no budge, still at 5k on the tach

 

[55trucker]

Pull off the intake snorkel to the throttle body, is the throttle plate completely closed?
Cover off the throttle body opening with some cardboard and seal it, try to start the engine........

what happens?

 

[danielp3344]

knowing what engine you have might help but at least on mine (2.9) there are three vacuum lines tucked under the throttle body where you could easily miss them. I'd ignore the IAC, pretty sure it can only get the engine up to maybe 2k. also maybe look for a large crack in the manifold? all that air has to come from somewhere...

Pictures of the throttle body and overall engine bay would be nice

 

[Sludawg40]

knowing what engine you have might help but at least on mine (2.9) there are three vacuum lines tucked under the throttle body where you could easily miss them. I'd ignore the IAC, pretty sure it can only get the engine up to maybe 2k. also maybe look for a large crack in the manifold? all that air has to come from somewhere...

Pictures of the throttle body and overall engine bay would be nice

I’m going to take a look at it tomorrow before heading to thanksgiving dinner and I can snap a few pics but the engine is a 2.9