What is the map sensor??what does it do?what makes it go bad?how can you tell when its bad?my cousins 97 tj is cutting out and knocking untill 3200rpm.please help were working on it now and need it to run right.thanks  

its manifold absolute pressure, its used to tell the ecu whats going on with the manifold pressure, its used to calculate the air density and the air mass flow rate, which is in turn used to determine how much fuel needs to be injected. if you dont know what it is, chances are a skilled mechanic needs to be working on it. take it in somewhere, its gonna cost some bucks but it needs to be looked at by someone who knows what they are doing  

My 1997 Grand Cherokee wasn't shifting right (automatic).  I took it in and had it scanned with the Jeep dealer computer.  It said MAP sensor - low voltage.  They cleared the code.  Brought it back in one week later same code.  I ordered a new MAP sensor.  As it was in freight, my catalytic converted became disconnected from my manifold and fell to the ground (luckily in a parking lot).  I'm guessing it was from the off-roading I was doing the weekend before the trouble started.  Once I re-connected it properly, the MAP sensor code went away, and everything is shifting right again.  Something to check.