An engine's MAP, which stands for manifold absolute pressure, sensor monitors the amount of pressure in the intake manifold, which is where air and fuel are introduced to the engine. The vehicle's throttle body helps to increase or decrease the pressure in the intake manifold by opening or closing a specific amount. The MAP sensor will adjust the amount of fuel versus air taken into the engine, based on its pressure readings.
Surging and Idling Problems
A faulty MAP sensor can affect the mixture of fuel and air going into the engine's cylinders to the point that the engine will surge under different scenarios. The engine will rev suddenly, possibly causing the engine to sputter and die. The engine can also surge while the car is sitting idle, such as at a traffic light. You may also notice the engine idles rough, meaning the RPMs fluctuate when the car is on but not driving down the road.
Fouled Spark Plugs
Because a faulty MAP sensor can cause the engine to produce a rich fuel mixture, you may also notice the engine's spark plugs are fouled or coated with a white powdery substance. You can try to clean the spark plugs or install new ones, but the problem will not be eliminated until you address the faulty MAP sensor, which is reading the air and fuel mixture incorrectly.
Loss of Power and Poor Fuel Economy
A MAP sensor reading the engine's air and fuel mixture incorrectly can also affect the engine's power output. If the engine has too lean a fuel amount compared to the amount of air in the cylinders, this will decrease the amount of burn and in turn the engine's power. This incorrect mixture can lead to the engine not getting as much burn from the mixture as it normally would, causing a loss in engine power. With the lower engine efficiency comes also a decrease in the engine's fuel efficiency, causing the vehicle to consume more gas than it normally would.