2004 Mazda MPV Van shakes uncontrollably

I've noticed that when I come to a stop light, with my foot resting on the brake, my van shakes and sputters uncontrollably. Rain makes worse.

Also have a problem with the engine turning off while driving, especially after using the air conditioning system or turning corners.

Have had this looked at by two mechanics, one said it was bad gas, the other said it was a sensor, which we had replaced, but did not fix the problem then he said it was the oxygen sensor. I am totally confused.

Please Advise