MAP Sensor

One of the most important sensor in Electronic Fuel Injection (EFI) engine (Alza 2010) - to calculate mass air flow as well as fuel flow rate. 

1. Engine on idle MAP sensor reading = 20 in-Hg (Scan tool OBD2 will read about 8~9 in-Hg)
2. The data is used to calculate air density and determine the engine's air mass flow rate, which in turn determines the required fuel delivery for perfect combustion. 
3. Typically found in fuel injected engines, the manifold absolute pressure (MAP) sensor is one of the sensors an engine control module (ECM) uses to calculate fuel injection for optimal air-fuel ratio by continuously monitoring intake manifold pressure information. Making sense of your sensors: MAP sensor | Delphi Auto Parts
4. At sea level, atmospheric pressure is about 14.7 psi (pounds per square inch). When the engine is off, the absolute pressure inside the intake equals atmospheric pressure, so the MAP will indicate about 14.7 psi. At a perfect vacuum, the MAP sensor will read 0 psi. What should map pressure be at idle? – MVOrganizing
5. Look for these warning signs: Rich air-fuel ratio: Look for rough idle, poor fuel economy, slow acceleration and a strong smell of gasoline (especially at idle) Lean air-fuel ratio: Look for surging, stalling, lack of power, hesitation on acceleration, backfiring through the intake, and overheating. What should map pressure be at idle? – MVOrganizing
6. The MAP sensor also provides a vital role in helping the ECM determine when the ignition should occur under varying engine load conditions. Making sense of your sensors: MAP sensor | Delphi Auto Parts
7. Whichever sensor your engine uses, the ECM will not be able to optimize fuel injection without accurate air mass information from a working sensor. And poor air-fuel ratio at the very least will cause performance issues and premature engine wear. Making sense of your sensors: MAP sensor | Delphi Auto Parts
8.  When you press on the gas accelerator pedal, the pressure in the intake manifold increases, resulting in less vacuum. The differences in pressure will flex the chip upward into the sealed chamber, causing a resistance change to the voltage, which in turn tells the ECU to inject more fuel into the engine. When the accelerator pedal is released, the pressure in the intake manifold decreases, flexing the clip back to its idle state. Making sense of your sensors: MAP sensor | Delphi Auto Parts
9. The ECU combines the manifold pressure readings from the MAP sensor with data coming from the IAT (intake air temperature), ECT (Engine Coolant Temperature) sensor, baro reading and engine speed (RPM) to calculate air density and accurately determine the engine's air mass flow rate for optimal air-fuel ratio. Making sense of your sensors: MAP sensor | Delphi Auto Parts

How does car get's air intake on idle?

It is one of the intriguing question linger in my mind before I knew about this. Yes where does car gets air intake during idle? Everything seems to seal closely tight and there is no way for the air to get in unless the gas pedal is press then the throttle body butterfly is wide open for air intake.

After a long search on Google and forums couldn't really found the answer until the OBD2 ELM327 Bluetooth ECU reader came. The data stream from ECU to the OBD2 read throttle body position on idle is always at 11.4% . Was a little surprised as the throttle body butterfly seems to closed tight on idle if you open the filter box to see. 

So it turns out the naked eyes can't really spot the throttle body butterfly valve opening at 11.4% on idle. This data is read by the Throttle Body Sensor (TPS) monitoring the position of the butterfly valve. It's very interesting to know!!. Therefore next time if you notice any value that is way less or too much more than 11.4% on idle either the engine will jerk and die (too low = butterfly valve opening too narrow) or sound like helicopter (high rpm = butterfly valve opening too much).