[shorod]

The "plain engine" and I believe 8th VIN of U is the "Vulcan" 12V engine. The Duratech is the 24V engine, but I'm not sure of the VIN.

The factory service manual hints that a P1504 indicates that the IAC motor is likely shorted to ground. If you measured lower than specified resistance, that is an indication that you may in fact have a shorted IAC to ground.

There are a few ways you can check the operation of the IAC motor. You can try unplugging it and seeing if that has any effect on the way the car starts, idles, and/or runs. If it does not, that is a good indication the motor is shot.

You can also turn on the defroster or A/C (if the ambient temperature is above freezing) and see if that causes the engine to speed up or bog. If the engine bogs, you probably have a bad IAC.

The engine should also speed up slightly if you turn the power steering all the way to lock and hold it there for a couple of seconds. You don't want to hold the steering at either of the locks for more than 5 seconds or so as that could cause damage to the power steering pump. If the engine bogs or stalls, you probably have a bad IAC motor.

As for checking the fuel pressure, I'm not sure on that particular engine if it requires something special, but I would be surprised if it did. Maybe someone else on this forum has checked the fuel pressure on the same engine and has some pointers for you.

-Rod