Give at least two results of too little air being in a running engine.

The answer is:

Low power output Thick exhaust fumes

Due to little oxygen, the fuel does not burn completely and therefore only a small proportion of power of the fuel is harnessed to turn the pistons. This can even cause the engine to stall. Due to incomplete combustion, because there is more fuel than oxygen in each combustion cycle, the exhaust will be darker due to unburned carbon.