The "valve clatter" is probably pinging. Typically, an increase in idle speed and an increase in pinging is associated with the spark being advanced too much. You could put a timing light on it and check it against spec., but that's is assuming the outer ring of the damper pulley hasn't slipped on the rubber cusshion sometime in the last 16 years.

I don't know how the timing could have gotten out of whack with a distributor replacement , unless the tech screwed something up. I was always told the timing wasn't adjustable - that the computer controlled it per RPM input, load input, knock sensor input, driving pattern, etc, etc.

Does the car have a cam-driven distributor or is mounted on the side of the engine?