1986 Pontiac 6000 STE Idels Rough

Best to have codes read if the engine light is on. start up and rough idle are different. Rough idle can be different things. When is the last time you had a tune up?

Black smoke at times is a indication of a rich running condition, This is where a mechanical condition of the enigine is necessary such as the compression test

Idle air control valve and possibly the throttle position sensor contacts are worn the both of them expand from heat and break contact but try first using carbon conductive grease on the plug contacts there could be oxidation or corrosion in them causing the problem before you start spending $$$$ you spent big money already with no result ?good luck stephen

check the Idle Stop Solenoid

Check the intake hose to make sure that it doesn't have a whole in it also check the air box that the filter goes in also. Mine was idling rough also and we found a whole in the filter box and the intake hose had a whole in it. Hope this helps.

1988 ranger 2.9 runs great cold then after a few minutes when warmed up hesitates with intermittent black smoke from the tail pipe until i hit the the throttle then clears and will repeat this behavior...

I would think the most likely culprits would be a bad EGR or TPS

well you could try to get a vacuum gauge and see if your car reads what it supposed to and if you buy one it could tell you what it could be.

Have you ever changed the fuel filter? If it's not that, and it's not a vacuum leak, it is probably your idle air control valve.

Try cleaning the Idle Control Valve by removing the air cleaner duct work and buying carb cleaner and to the fuel side system there are two holes to the sides of the cylinder. Spray directly at these holes with the engine running at about 1200 rpms. Spray a good bit of it about 10 seconds. Then turn off the engine and let the cleaner soak. Repeat the process a few times. See if this works for you.
If not the idle position sensor may be bad. Get a trouble code at any Autozone or similar store for free.