Are you driving an Isuzu built after 1980?  If so, then your Isuzu uses an oxygen sensor.  Your Isuzu oxygen sensor is an essential part of your emissions control system.  It sends vital information to your engine's management control system.  Your vehicle is able to maintain low emissions and run efficiently, thanks to the oxygen sensor.  There is a perfect ratio of air and fuel that must be reached and maintained in order for your engine to run efficiently.  Too much air in the mixture is called a lean mixture.  Too little air is called a rich mixture.  Both situations will cause performance problems.  Therefore, when your oxygen sensor detects too much or too little air, it sends that data over to the engine's management computer.  The computer will then adjust its fuel output up or down to reach the proper ratio.  A broken oxygen sensor will result in poor acceleration, surging, hesitation, emission test failure or poor engine performance.