You may have either an obstruction in the air intake tract or even more likly the exhaust tract. Catalytic converters tend to fail with the age of your vehicle and when they do they collapse in and block the exhaust path restricting it. You may have clogged fuel injectors. Try running a can or 2 of SEA FOAM or BG44K and give the deposits it lossens time to break free and see if performance improves. There could be a timing issue with the crankshaft position sensor, CKP or the camshaft postion sensor CYP. Sometimes putting a timing light on the engine will tell if this is an issue but it is usually a problem once RPM attempt to go up that the ignition gets advanced and if either sensor has problems it will cause stalling issues. You can also check the throttle body for carbon deposits and butterfly movement. If it needs cleaning use carb cleaner but make sure to spray ports from the outside in towards the inside or towards the intake tract. This prevents depeosits from moving deeper into the port tract and the best chane of loosening and getting them out is to clean it this way as they build up on the inside of the throttle body.
You could also have a vacuum leak which will make a hissing or whistling sound from air being sucked in. I am giving you a link to a walk through diagnostic on engine stall problems.
Here it is;
Thursday, December 22nd, 2011 AT 11:41 PM