Volvo: 86 240 wagon bucking stalling, air fuel mixture, mass airflow sensor

Question
I have a 86 240 wagon with approx.240k miles.This problem is getting worse. It started as intermittent.
While driving the car will start to buck, hesitate and stall when the clutch is pushed in at a stoplight or stop sign.I have changed the wires, distributor cap rotor plugs and fuel filter.The car may not act like this for a few days and then for several days will run like this.Today it was idling very fast on my way to work in the AM at about 40f. After work on my way home it was idling very rough and blowing black smoke[rich] out the tailpipe.I am running out of ideas.Oh yea I also removed the fuel press. reg. there was no fuel in the vacuum side and it seemed to hold a vacuum when applied.  

Answer
It sounds like you might have a pretty gunked up throttle body.  It happens with high mileage cars, and in your case, if it has never been cleaned out, can definitely cause intermittent problems.  Also, check to make sure your in-tank fuel pump is functioning.  If it has failed, or just suffers from an intermittent short, it causes the main pump to work harder and usually starves the engine for fuel.  Finally, I would check your mass airflow sensor and  your oxygen sensor.  A failure of either one of those can cause bogus readings to be sent to your emissions control computer, which can in turn cause the engine to be fed the wrong air/fuel mixture, again causing a drop in performance, a gas smell, and black smoke out the back.  Good luck!