[CSHADES]

The first thing I would check on this before throwing more parts at it is the actual vacuum reading. Do you have 18 inches of vacuum at idle or at least close to that and what is the reading at about 2500 rpm? The MAP sensor is one of the main inputs as far as fuel delivery on these old obd1 systems, the ecm will ignore the o2 sensor readings if it thinks you are under a heavy load/low vacuum situation i.e. wot or close. If the vacuum is low I would look at either a timing chain problem or maybe a outer ring slippage on the balancer that make the timing look correct when it isn't.