This page contains information in regards to VAM AFM sensors.

Depending on the company discussing this item, VAM stands for either Volume Airflow Meter, or Vane Airflow Meter. It is a type of AFM (AirFlow Meter) that uses a spring-actuated vane in order to read airflow entering the engine.

As airflow increases, the vane opens further. The vane is attached to an arm that makes contact with a variable resistor pad (a potentiometer).

Modifications

Spring Tension Adjustment

Absolutely NEVER adjust the spring tension from the factory position. It affects the entire operation of every single aspect of the vehicle. It will not only provide your engine with incorrect fueling, but incorrect ignition timing, incorrect idle detection, incorrect ignition correction, incorrect filtering factors, and anything else that is controlled by intake airflow (which is directly translated to engine "load"). Never ever (never ever) adjust the spring unless you have a bench-flow machine and are correcting output to match OE specifications.

Compounding the issue of the initial erroneous airflow output signal, spring tension is not linear. This means that any small change you make in the lower operational ranges becomes exaggerated as the airflow increases. Adjusting the spring tension outside of OE specifications can lead to engine damage or even complete failure.

It is so important, it has to be said again... Absolutely NEVER adjust the spring tension from the factory position.

Cross Compatibility

A common upgrade for vehicles with the M20 engine is to use the larger diameter M30B35 VAM. This is generally worth about a 1-2% increase in engine output. However, it requires a specific tune to match the mapping of the different VAM. Do not use an M30B35 VAM on a stock tune, and absolutely do not adjust the spring tension of the M30B35 VAM to try and "compensate" for the difference. A tune with proper mapping is the only healthy and reliable method of running this modification.