Hello,
I just bought a 1977 Chinook Mini Motorhome from a mechanic who claimed to specialize in older vehicles. He told me that a lot of the Toyota trucks from the 70s had problems with the solenoid, so it was common to bypass them. This is what he did with ours, and as a result the engine runs on for a little while after shutting the engine off. It sounds and looks terrible, and it's hard to imagine that this isn't causing the engine some sort of harm. It is a stick shift, and I have discovered that if I just leave it in first gear and let it stall out, it turns off peacefully. However, I'm worrying that if I do this often enough it will come to cause damage to some part of the truck too. Does anyone know of the potential harm that letting it stall out could cause it if repeated often enough?

 

It should be fairly easy to install a new fuel cut solenoid so it shuts off properly. I am not sure what specific damage will be done, if any, but I agree dieseling or stalling out is not good. Dieseling might be bad for the catalytic converter if your Chinook even has one. If nothing else, stalling is unnecessary wear on the clutch, and putting a load on the bearings while the oil pressure drops. I doubt either will ruin a 20R anytime soon, but it would be worth fixing and also check to see if the mechanic rigged anything else that should be fixed properly.

 

Did this fix your problem? Mines been dieseling and has a high idle(2500). Gave it a tune up, replaced vacuum lines and set the timing to just above spec... plus tuned the carb. the best It still diesels but only when it’s hot. It’s at 1100 respectfully but need it to be @ 750 to pass Cali smog. Thanks

 

Yours could possibly be a different problem than the original poster. The high idle will lead to dieseling if the throttle plate is out of the idle circuit. The anti-dieseling solenoid should not cause a high idle by itself, but if it is stuck in the off position then someone might have adjusted the idle high enough to get out of the idle circuit since the idle circuit essentially does not work anymore. With the key on, you should hear the solenoid click when the harness is unplugged and plugged back in again. If it does not work and you cannot find a replacement before you need to smog, I am sure it can be rigged open so you can use the idle circuit again and set it to spec. That should not have an effect on smog, but it will cause it to diesel when the key is turned off.

If the solenoid works and you cannot adjust the idle below 1100, then look for anything on the throttle linkage that could be hanging it up. Could be something causing it to be stuck on fast idle. The choke linkage might be stuck, or the choke might not be opening all the way for some reason. Also make sure that all the vacuum lines are routed correctly. Maybe an idle-up valve is getting vacuum when it should not. If everything there is ok, then it is most likely a vacuum leak. Try searching for it with an unlit propane torch or a bottle of carb cleaner. If everything else is fine, the idle circuit might be plugged and the carb needs to be rebuilt.