Rough running 91 Sunbird

I am driving a 1991 Sunbird with the 3.1 and a 5 speed trans and at times it will run really rough and will belch black smoke out the tail pipe like it is flooding. It has set a lot of codes when it does this such as, coolant sensor, MAT, ESC, throttle sensor, etc. It seems that it sets up a series of codes but I checked out all of the sensors and they are O.K. The alternator is fine and so is the battery. I checked all the injectors and EGR, plugs and wires. The car will suddenly straighten out and drive nice again. I am thinking it is either the electronic spark module and the coil pack or the computer gets confused and craps out. This is an intermittent problem and is very hard to diagnose. Has anyone else experienced this. Oh ya, as I was looking around for answers while it was running, it just quit and then I started it right back up again, it idled for about 5 minutes then quit again. I took it for a drive and it worked fine. I have checked wiring and I cannot duplicate the problem by unhooking some of the sensors. Please help!! Thanks in advance.

Somebody? Anybody out there have a clue? This is driving me crazy!!!!

Take the ECM out (mark the plugs) and give it a good slap and put it back (this is how the pros do it).
Check all your ECM and ignition grounds on the engine block.
GM ECMs are plug-together circuit boards with plug-in chips-enough vibration and hot/cold cycles and they can get weird on ya.
You didn't say how you checked the sensors and injectors so I assume you scanned the ECM, used a noid light on the injectors and/or removed them and pressurized them/test fired them to check for leakage/spray patterns.
Black smoke and chugging is a sure sign of an over rich mixture.
If that engine has a cold-start injector, it may be stuck open or leaking when it's supposed to be shut.

Take the ECM out (mark the plugs) and give it a good slap and put it back (this is how the pros do it).
Check all your ECM and ignition grounds on the engine block.
GM ECMs are plug-together circuit boards with plug-in chips-enough vibration and hot/cold cycles and they can get weird on ya.
You didn't say how you checked the sensors and injectors so I assume you scanned the ECM, used a noid light on the injectors and/or removed them and pressurized them/test fired them to check for leakage/spray patterns.
Black smoke and chugging is a sure sign of an over rich mixture.
If that engine has a cold-start injector, it may be stuck open or leaking when it's supposed to be shut.

Nope, it was none of the above. I had a bad intake manifold gasket, so I replaced it, then when I put it all back together, I somehow pinched the wire going to the alternator because it is so damned tight in there and once in a while it would ground out and send the ECM into a frenzy. I moved and repaired the wire and everything is fine now. I have long since sold the car. No more used cars for me.

Heh. OK, it was electrical. Glad ya found it.