truckcoach i had a Detroit that was doing that it was rust on the inside of the plug going into the ecm the ecm though i had my foot on the clutch so sometimes the jakes, cc or high idle wouldn't work. took it to 3 shops before someone LOOKED IN the plug and found it. volvo saids not necessary to high idle a volvo d12, the egr system keeps it hot enought 530k and still on the same turbo and dino 2 months ago said she's fine.
Every once in a while I see these little rods in a truck stop, some sort of extremely dangerous-looking contraption that would rest on the bottom of the steering wheel and a little adjustable peg leg or something would hold the accelerator pedal down, back in the stone age when the trucks didn't have cruise control. It looks like it would be a royal pain in the ### to use while driving, but if one of the old timers who reads this, can remember what I'm talking about, and explain it better, maybe tell you where you can still find one. I don't know where to get one but I imagine you could use something like that as a "fast idle", adjust it while watching your tach. Probably wouldn't be hard to make one, it looks pretty simple.
Checking the ecm plug is an awsome idea, especially since the truck was washed with the hood up 2-3 days before problem started!
mine would do it 30-48hrs after i hit a bad rain storm, it would go stuped for a few days to a week then it would start working when i got to the shop...? 1st time it was the wire (in the plug) that told the ecm i was on the breaks (no high idle, no cc,) 2nd time it was the wire (in the plug) that told the ecm i was riding the clutch (no high idle, cc, no jakes) this time when i got to the shop the first thing i told then to check was the plug and 45min later it was fixed. 3rd time the accelator stop working, 1.5hr later it started working , got to the shop and was fixed in less than 30min
I got a free truck automated truck wash at a Petro after some repairs in the shop one day. After I went through the truck wash, my front HVAC fan quit working. Only the one in the bunk would work.
BINGO !!! Have seen that happen with KW, Petes and IHC's. On my T800 I installed a small spring that pulls up on the pedal. Must have cost all of 35 cents for the spring.
Does your truck have a override switch? If so, press on it when the shut-engine light illuminates to bypass the shutdown.