First, what is your idle speed with the IAC disconnected? Did you set it to 480, but it increases to only 550 when you plug the IAC back in? If that's the case, it's pretty obvious your IAC is either clogged or simply not working. If the idle picks up at least a little when plugging in the IAC, I'd try soaking or spraying some carb cleaner through it before replacing it.
As for getting the timing right, RPM is irrelevant other than that it is high enough for the engine to run smoothly. You could use a clamp on the throttle cable to force the revs up if you need a higher speed for better stability. When the service connector is jumped, idle speed is locked, regardless of RPM.
As for getting the timing right, RPM is irrelevant other than that it is high enough for the engine to run smoothly. You could use a clamp on the throttle cable to force the revs up if you need a higher speed for better stability. When the service connector is jumped, idle speed is locked, regardless of RPM.
