12.14 Manifold absolute pressure sensor (IDA)
When manifold vacuum is high (idle), then the absolute air pressure in the manifold is very low, and the electronic control unit provides less fuel. When manifold vacuum is low (throttle wide open), manifold absolute air pressure is high and the ECM is delivering more fuel.
The intake manifold on MPI models is «dry» collector. Because no fuel enters the manifold, fuel is injected at the rear of the intake valve, so fuel cannot enter the intake manifold absolute pressure sensor to foul the diaphragm, and the fuel trap is not used.
A reference voltage of 5 volts is applied through a wire to the sensor, the second end of which is connected to «mass». The third wire is connected to a sensor that converts the intake manifold pressure signal into voltage. When the manifold pressure changes, the signal voltage returns to the electronic control unit.
Intake Manifold Absolute Pressure Sensor Voltage Values
Terminal numbers
See illustration 12.11
MAP sensor type
analog type (3 wire).
Influence of external factors
- Excess fuel in fuel trap or vacuum hose
- Vacuum leak (intake manifold or other vacuum hoses)
- Vacuum leak in intake manifold absolute pressure sensor hose
- Damaged vacuum hose or connection
- Faulty inlet or outlet valve
- Incorrect idle speed
- Incorrect ignition timing Defective spark plugs (large gaps)
Checking the MAP sensor (general check)
1. Inspect the MAP sensor multi-pin connector for signs of corrosion or damage.
2. Make sure the connector terminal pins are properly installed and making good contact with the MAP sensor multi-pin connector.
Checking the operation of the MAP sensor using an oscilloscope or voltmeter
1. Bend rubber seal to manifold absolute pressure sensor multi-pin connector (where possible) or connect output unit (WWII) between the multi-pin connector of the electronic control unit and the electronic control unit.
2. Connect the negative probe of an oscilloscope or voltmeter to ground on the engine or to ground terminal No. 1 of the MAP sensor.
3. Connect the positive probe of an oscilloscope or voltmeter to the signal wire terminal of the intake manifold absolute pressure sensor.
Checking the MAP sensor with a vacuum gauge
1. Disconnect the vacuum pipe from the intake manifold absolute pressure sensor.
2. Connect the vacuum pump to the sensor.
3. Turn on the ignition.
4. Compare the ignition voltage with the value specified in the specifications.
5. Create a vacuum, which is indicated in the table, and check the smoothness of the voltage change (see illustration 11.15).
6. If the voltage changes in steps, then see the subsection called «The output signal is unstable»
7. Disconnect the vacuum pump and use a T-piece to connect a vacuum gauge to the intake manifold and intake manifold absolute pressure sensor.
8. Let the engine run at idle speed. If the engine vacuum is low, check:
- Vacuum leak.
- Clogged vacuum tube.
- Engine-related problem, such as incorrectly installed toothed drive belt.
The output signal is unstable
1. An unstable output occurs when the output voltage steps or drops to zero, or an open circuit occurs.
2. If the output signal is unstable, this usually indicates a malfunction of the intake manifold absolute pressure sensor.
3. Use the pump to create a vacuum of approximately 560 mmHg. The transducer diaphragm must hold pressure for a minimum of 30 seconds at this vacuum.
4. If there is no signal voltage in the intake manifold absolute pressure sensor, then perform the following check called «No signal voltage».
No signal voltage
1. Check the supply voltage (5 V).
2. Check for voltage at the ground terminal.
3. If the power wire and ground wire are OK, check the continuity of the signal wire going between the intake manifold absolute air pressure sensor and the electronic control unit.
4. If there is no power supply and/or ground, check the continuity of the wiring going between the intake manifold absolute pressure sensor and the electronic control unit.
5. If the wiring of the absolute air pressure sensor in the intake manifold is in order, then check all the supply and ground contacts of the electronic control unit. If the contacts are in order, then the electronic control unit may be faulty.
Signal voltage or supply voltage at battery voltage level
Check for a short in the wire connected to the positive terminal (+) battery, or the supply circuit of the sensor.