There is not a vehicle on the market that is not equipped with at least one computer. The only necessary computer in cars are known as Engine Control Units (ECU). They are in charge of monitoring engine emissions and making adjustments to keep the engine's emissions as low as possible. Modern vehicles are equipped with many different sensors that send information about the vehicle to the ECU. These sensors include: mass airflow sensor, oxygen sensors, throttle position sensor, coolant temperature sensor, voltage sensor, manifold absolute pressure sensor, and engine speed sensor. (For more information view my sensor page)

The ECU uses information from these sensors to control the fuel injectors, spark plugs and the idle speed which allows the vehicle to get the best possible performance from the engine while keeping emissions low.

The ECU is always computing complex equations instantaneously in order to do many things in vehicles.

For example the calculation the ECU does to determine the pulse width of fuel in fuel injectors is:

Pulse width= (base pulse width) X (RPM) X (LOAD)