Q: Stalling at cold start, runs fine when warm

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I own a 1990 Chevy P30 Step-van (but was converted into a school bus and now I've converted to an RV). I've been trying to do some research on some things online about this, but it's hard to find information. My mechanic said I need a new Idle Stop Solenoid, but I was also reading that it could be the Idle Air Control Valve. They look similar on RockAuto and are similarly priced. I have a diesel 6.2 engine and a Turbo 400 transmission. I just got a new fuel injection pump. My mechanic tested if electricity was getting to the solenoid and it is.. but, that's not something you want to have power to all the time (if I understood him right, I could have completely misunderstood him).

Whenever I start up my bus, it'll stall unless I put my foot on the gas and rev it for a few minutes so it warms up. Once it's warm, everything runs fine.. but it's just those pesky cold starts.

Thanks!

My car has 217000 miles.
My car has an automatic transmission.

Diesels are in fact notorious for being cold blooded by nature and can be even worse on cold starts. This is mainly due to the manner in which diesel fuel is ignited vs regular gasoline. Diesel fuel has a much lower flash point than diesel does which also makes it particularly more difficult to ignite. What you are describing however, does sound like a dirty or failing idle air control valve. The idle air control valve reads the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and at idle. Since this valve is controlled by the vehicle’s computer, it will adjust idle speed based upon other measurements such as engine temperature, intake air temperature and electrical system load or voltage. When you accelerate, the engine RPM increases, and as you let off the gas, the RPM slowly returns to the normal idling speed with the help of the idle air control valve. When the engine RPM drops below the normal range of about ~800 RPM, this often times will cause the engine to stall indicating a dirty or faulty idle air control valve. I would recommend having an expert from YourMechanic come to your location to diagnose and repair your idle air control valve.

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