When I first got my '84 Targa the idle would occasionally surge up and down(embarrasing in traffic) and it would emit rich exhaust. Most of this went away after a mechanic "played with" the idle control positioner screw(twisted it back and forth). It still gets "fluffy" (rich) when started on occasion-a restart clears it out. While driving the car will jerk-the engine dies but momentum must restart it and the no problem again for days or weeks. Help!!