2000 LeSabre starts but runs very rough and stalls. After

My 2002 Lesabre (app 115000 miles) started something like this. Also the loose gas cap had been coming on for quite a while. I replaced the vacuum line from the air intake to the fuel sensor. It is under the engine cover (twist off the oil filler to remove the cover). There are two hoses together that come of the air intake. The small one goes to the top of the engine. The other goes across the front and makes a 180 turn back to the sensor. Chances are the 180 piece is cracked. It all comes from the dealer as one unit. $25
Seems to have fixed my problems. So if your car is running a little rough. Shutters under load. If the gas cap loose is coming on or probably a number of symptoms this might be the answer. I would replace this item. A cheap try.

Sounds like the plugs are not firing hot enough on initial start-up. Try a quick spark plug change, and clean throttle body. The gas being injected, isn't being burned fast enough by the plugs, which causes the car to have a hard start-up. You may try a higher octane gas or Lucas injector cleaner with your usual octane rating. Lucas comes in a very small bottle, and works very well in my opinion.