The vacuum inside an engine’s intake manifold, by comparison, can range from zero up to 22 inches Hg or more depending on operating conditions. Vacuum at idle is always high and typically ranges from 16 to 20 inches Hg in most vehicles.

Start the engine and check the reading; at idle, the MAP sensor should read 1 to 2 volts. This indicates the MAP sensor is responding to changes in vacuum. Digital MAP sensors are best tested with an oscilloscope. However, they can also be tested with a tachometer, which is a type of frequency counter.

The MAP voltage readings should range between 0.9 to 1.5 volts. This vehicle is high at times, indicating pressure pulses in the intake. Erratic RPM and MAP sensor readings normally indicate an internal misfire condition due to improper sealing of the cylinder.

A faulty MAP sensor will affect an engine’s air-fuel ratio. If the ratio is incorrect, ignition inside the engine will occur at an improper time in the combustion cycle.

If the MAP sensor goes bad, the ECM can’t accurately calculate engine load, which means the air-fuel ratio will become either too rich (more fuel) or too lean (less fuel). This leads to excessive fuel consumption, poor fuel economy, and possibly detonation.

It is not advisable to drive your vehicle with the MAP (manifold absolute pressure) sensor disconnected. With the MAP sensor disconnected, the fuel delivery will be excessive and could cause harm to the engine and exhaust system (catalytic converters).

Your engine misfires and shakes: If a MAP sensor reports a false high pressure reading, the engine’s computer will signal for more fuel. This results in a rich mixture, which can foul the spark plugs and cause a cylinder not to fire. A misfiring engine will shake and transmit that motion into the cabin of the vehicle.

Depending on the voltage from the MAP sensor, the ECU will fire the injector for a longer or shorter burst to deliver more or less fuel, as the case may be. The thing is, a bad MAP sensor won’t always trigger a check engine light or cause the computer to register a DTC (diagnostic trouble code).

The MAP sensor in a car will usually stick around for about 150,000 miles before conking out. If your car has that many miles on it, your MAP sensor isn’t going to be the last thing to give out on you. There are likely a lot of other car parts that might be on their last legs.

Use an electric parts cleaner on a soft rag or paper towel to clean the outside of the MAP sensor. Shake out the excess and let the MAP sensor dry. Check the MAP sensor vacuum hose or intake manifold port for additional contamination. Clean these with electric parts cleaner and a brush if necessary.