1987 astro 4.3 rich idle,ok at cruise replaced EGR,IAC,MAP,temp, new injectors, fuel pressure 16 lbs, new tune up, what could it be?

What is the 8th character in the VIN? A problem with the distributor cap, rotor, wires, plugs, oxygen sensor, air filter or ignition timing are the most likely causes, even a partially open or too cold of thermostat could cause a rich condition, just to name a few. Is the check engine light on? If so, what codes are in memory?