Fast and faster idle

[Bryan]

We are on our first trip since motor rebuild. Something really strange is happening. When we stop the bus, the idle stays really fast, the only way to stop it, is to turn on the "fast idle" switch which actually slows the RPMs down, then when we turn off "fast idle" switch it goes back down to regular idle speed.

Any thoughts?

[Scott & Heather]

What Engine did you have in there again?


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[Scott Crosby]

My guess would be that the rack is holding up or the linkage is holding up.  Check your return spring and I would disconnect the accelerator linkage at the governor to confirm its not in the governor or the rack.  The fast idle is forcing it back down.

[luvrbus]

Sounds to me like the Skinner valve is leaking by enough to engage the fast idle but not enough for the holding cylinder,then when you engage it there enough air pressure for the holding cylinder to work thus bringing the rpm back down. 

You turn it off and all is normal again for a while check your ground on the Skinner valve

[bevans6]

Another thing to check.  The fast idle switch actuates the skinner valve which sends air to two different air cylinders - the speed lever locking air cylinder and the fast idle air cylinder.  The speed lever locking air cylinder forces the speed lever to it's minimum setting, lowest speed.  If your throttle linkage is hanging up in any way this will pull past that bind and force the speed lever to close all the way.  So I suggest looking to see if something is binding and holding the speed lever open.

Brian

[Bryan]

We believe it is the throttle linkage sticking. It's only happened a couple times. Gonna use some WD 40 and see it fix the problem. Thanks guys!