High revs on startup

[Iheartbus]

So up until recently I've had no issues starting the bus, but today I had to drive it to get a hitch attached at a Fab shop and I noticed the engine revved very high and uncontrollably when I started it. I double checked to make sure the gas wasn't pressed. I put it from neutral to drive and it stopped. I thought I held the key in too long so I put it in neutral and tried again this time barely turning the key and it didn't seem to do it. Was it just the key or could there be more to it?

[Njsurf73]

Do you have a high idle switch?

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[Iheartbus]

I don't believe so

[Njsurf73]

Is it a conventional, fe, or re?

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[bansil]

what was outcome? this can help someone in the future.

what engine and layout?

Thanks

[Tarheel Travelers]

Originally Posted by Iheartbus

So up until recently I've had no issues starting the bus, but today I had to drive it to get a hitch attached at a Fab shop and I noticed the engine revved very high and uncontrollably when I started it. I double checked to make sure the gas wasn't pressed. I put it from neutral to drive and it stopped. I thought I held the key in too long so I put it in neutral and tried again this time barely turning the key and it didn't seem to do it. Was it just the key or could there be more to it?

I had the same issue with mine and I thought it was idling too high. I asked a mechanic and he said it may do that when it was cold. Mine was happening every time I started it so I just turn on the cruise control and decreased the “speed” even though I was parked and not moving and then it would idle at 800. After letting it sit for a month without starting it, the problem went away.

I’m interested in what people may think is the root problem. I have a FE, Mercedes 926 engine.


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[cadillackid]

it looks like the OP was a DT-466E. when the coolant and / or oil temperature are below a certain point at startup the engine will idle at about 900-1000 RPM as it shoots for 100 degrees f coolant temperature. as it gets closer to 100f coolant temp it will slow down.. the higher idle will stay active even in gear. though not as high.

this high idle will not be invoked typically when the oil / coolant temps are above 70 degrees at startup.

in Extreme cold. (seems to be coolant / oil temp below 20f) the engine will start and idle its first 30 - 60 seconds at a very low idle.. 450-500 RPM.. presumably to get the oil pressure up and circulating, then it goes to the elevated idle.

the T-444E will do the same thing.

your computer can also be programmed with an automatic warmup cycle.. the engine will run for a couple minutes at normal or slightly elevated idle as described above... and then will idle up to a max of 1350 to try and warm the engine to 170 degrees f. this is optional in the ECM and may or may not be enabled. this high idle will be cancelled when you press the brake pedal or engage the transmission or press the clutch pedal.

this above applies to Navistar 'E' engines.
not sure how cummins or Cat or MBE handle their cold weather starts.
-Christopher