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.