The mass air flow sensor on a 1998 Chevrolet S-10 is responsible for telling the engine's computer how much air is traveling into the throttle body. This is a critical to the proper operation of the engine, and if it fails, then you can have problems with the engine running correctly. A new mass air flow sensor is expensive though, so before you buy one to replace the old one, you can first test the one you have to make sure that the sensor is actually the problem.
Pop the hood. Locate the mass air flow sensor, which is on the intake tubing and has an electrical harness running into it. Pull the plug off of the sensor. Position yourself so the sensor is to the left and the harness receptacle is to the right. There are three electrical ports on the plug. From top to bottom, we will refer to them as "B," "A" and "C" on the bottom.
Adjust your multimeter to test voltage by turning the knob on the device to the voltage setting. Place one probe from the multimeter into the B port, and one in the C port. Turn the ignition on, but do not start the engine. Verify that the sensor is getting the same voltage as the battery is putting out -- approximately 11-14 volts. If it's not, then the problem may be the wiring to the sensor, or the VCM.
Adjust your multimeter to the frequency setting. Insert a probe into the B port, and another to the A port. Start the engine with the key. Allow the engine to warm up, then verify that the multimeter reads around 99 Hz.
Have your assistant slowly rev the engine up to the maximum RPM, and look at the multimeter. Verify that the sensor rises smoothly with the increase of the engine RPM, and make sure the multimeter reads 8,000 Hz. If the multimeter does not hit these numbers, then the mass air flow sensor may be bad.
