We recently picked up a 2003 Gruman Olson Workhorse with the L57 6.5L Diesel engine with 67k miles, and we initially only noticed a small rough idle so we took it to a local large diesel shop for a full inspection. They mentioned that it could be caused a timing pulley going bad, but then things got worse. In the last week it started surging when slowing or stopping, and occasionally it just completely stalls when at a stop, this happens almost every other day now. There's definitely a line leaking - I believe - engine coolant, and some of the vaccuum hoses appear to be damaged, but it didn't stabilize the idle when poking around with carb cleaner in the suspect areas. We ran a couple tanks worth of diesel injector/pump cleaner through, and tried resetting the idle, no dice.
My buddy and I aren't diesel mechanics so we're kind of at a loss here.
I've read that it could be the fuel pump at fault, the fuel injection pump, the fuel injectors, the fuel quality, etc. We've had people tell us it might be the air control, mass airflow, vaccuum lines, etc.
I'm looking for a little bit of guidance here because we've managed to repair our own vehicles in the past like our other workhorse with electrical and fuel pump issues, but that one was a gas engine so we don't have spare test parts. We don't have the money to just buy and replace each part until the problem is fixed either.
Feel free to ask any and all questions, I already appreciate you taking a glance