99 chevy cavalier 2.2 some1 please help me

im not a mechanic first of all lol but let me try and explain what i gathered overtime about my car problem. my brother has been doing mos of the mechanical work on this car and the check engine light is on all the time. he bought a diagnostic tool which told him after running for awhile that there is a fault with the MAP senson however it only showed up that once he cheked the voltages and the pressure and thy seemed to be consistent with what the book says it should be. however i want to know if despite this the sensor cud still b the problem. My symptoms are : when i slow down sometime like to turn corners it cuts off and if im reving it up in park it goes up so far and then like it makes a sound like it lost some pressure. Plz help i have changed sprak plug and wires, control module, the computer, fuel pump plus i have carried it to a couple mechancis who all gave different and even put it on diagnostics and still none that helped. when the car has cut off by itself i usually have to hold the gas pedal to the floor and try a few times b4 i can try it again. can some1 please give me an idea of my problem