Chevrolet Repair: 1988 k5 blazer, o reilys auto parts, throttle position sensor

Question
I have an 88' K5 blazer.  The truck is running extremely rich, I say this because the exhaust fumes are unbearable.  I have done some research and it seems like a sensor might be the first to check but which one.  The O2, coolant temp sensor, throttle position sensor?  Also when I am stopped at a light the truck kinda idles alittle weird.  Its not a steady beat if that makes sense.Any help would be much appreciated.

Answer
The O2 sensor would explain the richness. The idle if you mean that it stutters a bit is usaully normal too. For some reason those motors like to wear out the valves pretty quick, it's been my experience that there is usually something stuck in a vavle that causes the stutter. The coolant temp sensor is what tells the truck that it's warm enough and it can idle down off an engine start. Usually if the throttle position sensor is bad you'll be lucky to get it to start. I'm going to lean toward the O2 sensor as long as the timing is good. As far as the valves you have two solutions, run some stuff through the engine or have the heads redone. First what I would do is go to like Autozone or O'Reilys(auto parts stores)and ask for a can of Seafoam to clean the inside of the engine(combustion chamber, valves, stuff like that) not for the oil or anything like that. Have the manager, not an employee, I've never had good luck with people at the counters, take you out and show you step by step how to use the product(if used properly it works wonders although it may take more than one use) But one use should do the trick, if I was there I would show you how to do it but for now I am giong to have to rely on the fact that the "other" guys can help you.