Mass Air Flow (MAF) Sensor
Start the engine and warm it up to the normal operating temperature.
Check the voltage between the ECM terminal 51 (sensor signal) and ground.
If the ignition switch is on but the engine is stopped, the voltage should read approximately 0.4 volts.
At idle, the voltage should be 0.9 - 1.2 volts.
At 2500rpm, the voltage should be 1.5 - 1.9 volts.
From idle to about 4000 rpm, the voltage should be 0.9 - 1.2 to approximately 2.4 volts.
If the voltage is out of specification, disconnect the mass air flow sensor harness connector and connect it again.
Also check for crushed air ducts, malfunctioning seals on the cleaner element, uneven dirt on the element, or other improper specifications of the intake air system.
If everything checks out to be in proper working order, replace the mass air flow sensor.