I have a 1992 Buick Century with the 3.3L OHV 6Cyl Engine with 76,000 miles and I too have had these problems but my car doesn't stall every time I'm stopped/idle. It sometimes has difficulty cold starting especially during winter. Once it's started I will drive for about 20 minutes then the service light will come on. The motor will then cut out a few times but does not stall. The service light will turn off and the car runs fine for another 20 minutes. However, ONLY when the service light is on and need to stop for a stop light/sign it occasionally will stall but starts right back up and takes off. In this case there could be a number of things causing the vehicle to do this. I have a Diagnostic Tool that will make the service light blink out the code number(s) in which I will refer to the Service Code Definitions Chart in the book that came with the Diagnostic tool. Here are the codes that were present on my car which may be able to give you a better idea of what is wrong with yours. For each code there is a list of fault possibilities of what the problem(s) could be. Process of Elimination is pretty much the only option you have from this point on if you decide to fix it yourself.. Although there are still a lot of possibilities it is still narrowed down from having no idea. Just start with the most simple code to troubleshoot first and eliminate all possibilities for that code. Move onto the next if the problem has not been completely resolved. Hope this helps!
Code 16: - Battery or alternator problem - voltage too high or low - Direct ignition system (DIS) fault line open or shorted to ground - Ignition system fault - loss of 2X or Low Resolution Pulse signal - Transmission speed error
Code 22: - Throttle position sensor (TPS) - signal voltage is low - Fuel cutoff relay circuit - open or shorted to ground
Code 34: - Mass air flow (MAF) sensor - signal voltage or frequency is low during engine cruise - Manifold absolute pressure (MAP) sensor - signal voltage is low during ignition on - Pressure sensor circuit - signal voltage too high or low (carburetor engines only)