I've been trying to read stuff on here about high and low idle but can't quite find an answer to my questions so I thought I'd just ask! Is there supposed to be a high idle when I start my '93? When it's cold, it idles at about 600 rpm and when it's warm, it goes up to about 750-800. If I rev it up to 875 rpm, it smooths out and the windows quit rattling. It seems like when it's cold, it should idle faster, but if I turn the idle up, I don't want it up to 1000rpm when it's warm. Is there more than one adjustment?
Thanks!

 

On a mechanically injected diesel engine the high idle RPM is maximum achievable engine speed. The common adjustments on mechanical IPs are idle (low idle), high idle and governed speed (or max engine speed with a load). For instance, I just came inside from a tune up on Cummins NTC440 and the idle speed is 650, no load is 2350 and governed is 2100.

What I did on the 91 was install an aftermarket cruise control which allows me to idle the truck up to any RPM up to the high idle limit. You could also just install an solenoid to pull the throttle lever a preset amount to give you a high idle for cold weather.

Most mechanical engines will idle low when cold until the combustion temperatures come up and the engine is fully burning the fuel. So your cold 600RPM is normal. That NTC I mentioned earlier will just barely run on its own about 300-400 RPM when it's cold, idles normal after a few minuets of run time.

 

I set manual trans trucks to idle at 850 hot, it helps with the shakes at cold idle.