Cold weather has arrived here (-8c, 17F). Last night I had the truck plugged in for about 2.5 hours before start. Started fine, slightly high idle, slightly loud. But today after sitting 9hrs in the blowing cold UNPLUGGED, when it started, there was no high idle, just 650rpm, a little loud yes but not as loud as other "warmer" days (maybe around +8c, 46F) where I've seen it high idle at almost 1000rpm.

My question is that why does the high idle not happen when its really cold? I would assume that the colder it is, the more likely I am to get a high idle.

Also, it sounded like the batteries were struggling a bit, but it still turned over in a timely fashion. The batteries are only 6 months old(but they are made and I bought them in Mexico, covered in dust) and all my grounds are clean. Normal sounding? I'm running 15w40.

But more importantly, where is my high idle?

I'd say that 15W40 is your problem. When it turns to winter, I run 0W30 in all my diesels.

I don't think the weight of your oil has anything to do with your high idle not working - even though you probably should be running something 'thinner'.

On my old mechanical truck it has a sensor right on top of the front coolant crossover - kinda on the passenger side of it that's connected to a high idle solenoid. Not sure if you can unplug that sensor to make it think it's really cold out...but you could try it to test it(the sensor). On mine, you have to turn the key on, press the accelerator one time to set the high idle, then crank.

Odlaw, yep, that's the ole way of doing it. The newer OBD-I and II systems use a sensor for coolant temperature that calls the shots on timing, glows, TCC lockup, etc. etc. Somewhere on here there is a listing of ohm values vs. temperatures to check to see if it's within tolerance.

Was it 17* when you started it up after the 9 hours, or was it warmer by then? I would think you would still get at least a little high idle, but if it started fine it might be OK. Remember, the truck doesn't care about wind chill - just the actual temp.

With ECT sensor disconnected (on coolant xover) ecm supposed to default to -40 & give more advance,longer glo time & high idle . Easy enough to disconnect & see what happens .I think the high idle on mine is somewhat inconsistent.I put it down to varying temps.

Did you happen to run the glow plugs, turn the key off, and then back on again to run the glow plugs again? I tried that on mine once just for the hell of it (i dont have cold start problems) and it did not go into high idle that time.

Did you happen to run the glow plugs, turn the key off, and then back on again to run the glow plugs again? I tried that on mine once just for the hell of it (i dont have cold start problems) and it did not go into high idle that time.

Bingo, I think that might be why! I do that sometimes cus I think it might help warm things up a bit more.....come to think of it, that might be what i did every time I didn't get a high idle.

I also tried to start it with the remote start and as posted in another thread it didn't crank it long enough. So when I got in, I had to reset the key to start again.

I