Just bought this truck, 135 k miles 4x4, 350 auto. Kept hearing a bearing noise, toward the front of the engine. Replaced water pump, power steering pump, and put new bearings in alt. The noise is not in the engine, the truck has a remanufactured tranny about 5 k miles ago. The truck idles at normal op. temp in park around 500-600, in gear it drops all the way to 100-200. when i increase the rpm to 400 the noise leaves. I replaced the original plugs, wires , cap and rotor button as well. After which i developed a miss, at idle, however when i increase to 400rpm it leaves as well. There is a cap over the set screw adjustment, but would it be reasonable to think that the tranny specs of the reman are not the same as the factory tranny specs and could be putting more drag on the engine? of course the dealer wants to run diagnostics for 55 an hour. With it only needing a small increase in rpm would it be ok to drill the plug cover, bump it up to 400 in gear? dont want to mess with the timing, truck runs too good. Does anyone know what the recommended idle is for this truck? thanks chris

I presume this is an electronically controlled engine. If so, the Idle Air Control motor (IAC) will set the idle speed. There is an adjustment procedure for setting the idle and it's more complex than simply adjusting the screw. Almost sounds like your IAC motor may be bad. What you really need is a diagnostic tool and an IAC troubleshooting / idle speed adjustment procedure.

As for the noise, have you tried removing the serpentine belt and starting the motor breifly? Don't run it long because the water pump won't be pumping. That's a good way to isolate accessory noise. Unfortunately those serpentine belts run everything, so if you confirm it's accessory noise, it's more difficult to figure out which accessory it is.