Nissan Repair: Intermittent idling problem 98 Altima, vacuum system, trouble code

Question
Intermittently when I come to a stop, the engine idle drops drastically, sometimes it comes back up, but usually the car dies.  The car will start right up, but gas has to be applied to keep the idle up until you can start moving again.  It eventually clears up until it happens again, which now is once a day.  I have also noticed that I can tell when this will happen at a stop because while driving the engine will run a little rough, like a cylinder isn't firing.  My mechanic has replaced many sensors and solenoids, in the fuel vacuum system, but is still happening.  The check engine light goes on within a 100 miles of driving after a part has been replaced and the system has been reset.

Answer
Sorry to ask this, but I feel I have to.
Is your mechanic ASE certified?
Do you have the old sensors and solenoids?
There are tests on these parts that can be run prior to replacement.
What is the trouble code that is stored in the computer?
How did your mechanic reset the check engine light?