C230 P0170 Fuel Trim Malfunction Code
 

My 97 C230 sets P0170 code. Does any one know what sensor ( or part) is related to this code so I can do some diagnosis on it. I saw a posting years ago in this forum, the issue was taken care of by replacing the Mass Air Flow sensor. Since it would cost $400, I hesitate to buy one without confirming the MAF sensor is the problem. Any professional inputs will be apperciate!.