Volume Air Flow (VAF) Sensor
- Using test harness, or backprobing, connect lab scope pick-up to VAF sensor connector terminal No. 3. With key on, engine off, output frequency of VAF sensor should be zero. If other than zero, malfunction is in VAF sensor or ECM/PCM.
- Start engine. Compare waveform to normal waveform. See Fig 1. Waveform should be stable with frequency increasing as engine speed increases. A VAF with internal damage will show an unstable pattern with non-uniform frequency. An ignition leak during acceleration may temporarily distort the waveform pattern on a good VAF sensor.
- Using scan tool, or lab scope, compare VAF sensor output frequency with standard values. See NORMAL VAF SENSOR FREQUENCY VALUES table. If idling is possible even though VAF sensor frequency is outside normal values, fault is probably outside of VAF sensor. Check for intake air restrictions or disturbances. Check for intake manifold leaks, ignition problems and compression.
NORMAL VAF SENSOR FREQUENCY VALUES
| Application | Idle - Hz | 2500 RPM - Hz |
|---|---|---|
| Diamante 3.5L | 28-54 | 80-120 |
| Eclipse 2.4L & Galant 2.4L | 25-51 | 80-120 |
| Eclipse 3.0L & Galant 3.0L | 17-46 | 63-103 |
| Lancer | 10+ | N/A |
| Mirage 1.8L | 18-44 | 68-108 |
| Montero 3.5L | 17-43 | 64-104 |
| Montero Sport 3.0L | 25-51 | 74-114 |
| Montero Sport 3.5L | 18-44 | 58-98 |