Brian,

I would do all of the above. You might consider replacing all the rubber parts of the intake system. If is rubber and has been exposed to 16 years of engine heat, it is a potential vacum leak.

You might also resolder or replace the OVP relay.

If you still have the problem after all this, test (or have tested) the airflow sensor position indicator. Mine caused a problem exactly like you describe. They are now available by special order as a separate item so you do not have to buy the entire airflow meter.

Good luck and let us know.