C4500 high idle at cold startup

[Mark Rinker]

Started the C4500 this morning at about 18 degrees. Truck started normally, then after about 5 seconds, revvs to 1500 RPM and exhaust brake actuates (?) with switch in 'OFF' position.

Not liking the roaring fast idle on a cold engine, I step on the accelerator, and idle comes back down to normal. After a few seconds, it revvs back to 1500, and exhaust brake actuates...

5 minutes or so of this, and finally the truck is warm enough to where input from the footfeet keeps it at a more reasonable cold idle.

I have heard of cold high idle settings, but this seems WAY too fast for a cold engine, and wondering what the exhaust brake acutation is all about?

[JohnC]

Did you figure it out? My 06 2500 has some sort of fast warmup function that raises the idle and closes the vanes in the turbo to speed warmup. I don't have it enabled, so I don't know if it's exactly what you're seeing, but it sure sounds the same. It cuts off if you touch the throttle. Oh, and we don't have exhaust brakes... Wonder if EFI live could make one for me? :)

[mr. monte]

it's actually better for a cold engine to idle that high when cold, the oil is thick and harder to be "thrown" up to the cylinders to lube them, the exhaust brake kicks on to restrict the exhaust to aid in warm-up

if it's like what my LBZ does, it waits a few before it kicks up the idle, giving it a chance for oil pressure to come up

[Mark Rinker]

I've decided to trust the GM engineers and let it be. Seems odd, however, that it will return to the fast idle after the truck has been driven 100's of miles and has been warm for many hours. Will do it when temps are in single digits and truck is sitting during a delivery stop.

???

Probably need to have a winter front made for the truck.

[mr. monte]

the engines cools down cause it's not working (underload) when it cools down to a specific temp, the computer kicks the high idle back on, our 2000 powerjoke does the same thing

[Mark Rinker]

This function wastes LOTS of fuel. I am limiting warmup time, and starting and stopping the truck even during short stops, instead. The idle is too high, the air brake noise too loud if in my residential driveway at 5:30 AM, with neighbors still sleeping.

[JohnC]

On the 2500 you can disable it through the DIC. Don't know if you're so lucky...

[Mark Rinker]

DIC-less. :mad:

[DmaxMaverick]

DIC-less. :mad:


That's unfortunate.

But you do have a PTO throttle control, don't you? If so, set it at a lower RPM (800?). It should override the high idle.

[Mark Rinker]

Yes there is a PTO throttle control switch. Since I don't have a PTO system, it doesn't get much use. The first trip out with the truck, I bumped it and it took me awhile to figure out why my truck wouldn't go very fast...

[Mark Rinker]

The PTO switch does override the high idle. Thanks for the info, DMax its always fun to learn a new trick...:p

[JohnC]

Just for grins, I turned mine on. It's actually sort of neat. Definitely speeds up the warming. Before it really didn't make sense to let it warm up because it didn't warm up. Now it does. And the whistle is sort of cool, too! :)

[murphyslaw]

my '05 5500 lly does the same thing. when I start it it runs for a min then bumpes up to 1200-1500rpm until it reaches normal temp then drops to normal idle. if it cools off(idling in -20) it will bump back up to make heat. I thought it was a bit fast for a cold motor to, but its a normal thing so I figured oh well.

[Braveheart]

You can turn this feature on and off I believe...I remember seeing something in the manual about it. My 07 C4500 does the same thing.

[JohnC]

Mark:

did you ever figure out how to disable this?

Try this:

Key on engine off.

Depress the accelerator to the floor and hold it.

Apply the brake 3 times in 8 seconds.

Release the accelerator and start the engine.

(Hope I got it right...)

This will toggle the feature on and off on the 2006 2500/3500 without DIC.