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FAQ – Questions regarding MAF, IAC and TPS

MASS AIR FLOW METER (MAF)

1. How do I know that my mass airflow sensor is faulty?

The vehicle indicates errors such as erratic engine operation, reduced performance, increased petrol consumption and engine cutout.
Other causes may be possible why an intact mass airflow sensor may indicate wrong signals:

  • Defect exhaust gas recirculation valves
  • Leakages in the induction tract
  • Blocked air intake filters
  • Faulty tank ventilation valves among other things.

Only car garages are capable of conducting distinct fault diagnoses and reading out the error messages.

2. Why is my mass airflow sensor faulty?

Mass airflow sensors are extremely sensitive replacement parts. The hot film meter inside the mass airflow sensor is very susceptible and can be easily contaminated by dirty and oil. This may be due to different reasons. Environmental conditions (rain, splash water…), sand, dust, road salt, vibrations, oil and so on affect the efficient readings of the mass airflow sensor. Oil particles from oil covered sports air filters may damage the sensor. A faulty or damaged mass airflow sensor sends the wrong input signal to the electronic control unit which in turn wrongly activates other components. Regularly replacing the air filters helps to extend the durability of the mass airflow sensor.

3. Why does my car need a mass airflow sensor?

The mass airflow sensor measures the air mass, which flows through the air filter to the engine. The data is then sent to the control unit in order to specify the injection rate of the fuel. The combustion engine requires 14,7 kg of air for the optimal combustion of 1kg of fuel. In order to regulate the correct proportion of fuel and air in any operational condition, the engine control unit requires the exact information concerning the intake of the air mass. The mass airflow sensor plays an integral part in the reduction of exhaust and air supply.

4. What does a mass airflow sensor consist of?

A mass airflow sensor consists of a case which is positioned between the air filter and air pipe. The sensor is either screwed or firmly attached inside the case. The sensor in turn includes a hot film meter and electronics. The sensor measures the air which flows to the engine through the air filter and sends the data to the control unit.

5. Is it sufficient to use cleaner of the breaks or other cleaning agents to clean the mass airflow sensor?

The sensor membrane may be severely damaged by the clean up. Never apply compressed air as this may also damage the sensor.

5. Is there a difference between air volume sensor and mass airflow sensor?

No. Air volume sensors and mass airflow sensors refer to the same item. Other terms are hot film meter, HFM, airflow sensor, MAF or MAFS.

6. Why is it recommendable to fit a hot film meter instead of a hot wire sensor?

One distinguishes usually between hot film meters (HFM) and hot wire sensors. The hot film meter is not as sensitive as the hot wire sensor. Deposits accumulate often on the hot wire which affects a correct reading. Our offered product range specialises solely on hot film meter sensors.

7. Why are the prices at MAF Service GmbH more favourable than at other vendors?

Unlike other vendors, we have specialised exclusively on mass airflow sensors and offer these for selected car models only. This enables us to purchase larger quantities and allows us to keep reduced storage and administrative expenditures, which benefits our customers.

However, other brands have no bearing on the quality of our products. Our mass airflow sensors are subject to regular quality controls, so we can deliver the best in quality to our customers.

8. Is it sufficient if I exchange just the sensor or do I have to replace the entire case?

In cases where the mass airflow sensors are screwed to the case, you should definitely replace the entire mass airflow sensor. Otherwise, according to manufacturers, the sensor could be placed in the wrong measurement position, in addition to the old dirty case, and affect the readings. Hence, the guarantee would expire if the sensor was removed from the case.

What do I have to pay attention to when fitting a new mass airflow sensor?

We recommend that you exchange the air filter before you fit the new mass airflow sensor! A grubby or inferior air filer is often the cause for damages of the mass airflow sensor. The air-filter-housing should be exhausted – not brushed out.

A faultless air filter increases the efficiency and durability of the mass airflow sensor. The air filter should be replaced around every 25,000 km.
Please pay attention to the mounting direction. The arrow on the case indicates the direction of the air flow (from the mass airflow sensor to the engine).

The error memory does not have to be erased on purpose. It may be that your control unit resets the error memory only after a 100km.

9. Airflow meter, MAF, hotfilm sensor,… – what’s the difference or is it all the same?

MAF, hotfilm sensor, HFM, air flow meter sensor, mass airflow meter and others are all synonyms for airflow meter. Americans mostly call it MAF which stands for mass flow meter or sensor, Europeans prefer calling it airflow meter.
AFM is just the abbreviation for airflow meter.
Hotfilm sensors are airflow meters that use the hotfilm technology, which is more exact than the old hotwire technolgy.

IDLE AIR CONTROLS (IACV)

IDLE AIR CONTROLS (IACV)

10. What is an Idle Air Control and what is its function in the car?

The idle air control valve (IAC or IACV) also called idle speed control (ISC) or stepper motor is used on fuel injected engines to control idle speed. The stepper motor type of IAC features a pintle, which is used to either block or open throttle air passages. The powertrain control module (PCM) controls stepper motor operation.

11. Which are the symptoms of a broken IAC/Stepper Motor?

Not surprisingly, a broken IAC often results in engine idle problems. An engine that is idling too fast or too slow may point to a faulty IAC. An engine that stalls out may indicate IAC problems as well.

12. How can I check, if my IAC/Stepper Motor is broken?

Typically, if there is a problem with the IAC or its control circuit, the PCM will set a diagnostic trouble code (DTC) and turn on the check engine light (CEL). If the light is on, you can plug a diagnostic scan tool into the diagnostic port under the dash and read the stored trouble codes. If the codes indicate a problem with the IAC or its circuit, a vehicle specific repair manual should be consulted for further testing.

13. How do I change the IAC/Stepper Motor in my car?

IAC replacement varies from vehicle to vehicle, but it is fairly straightforward in most cases. Vehicle specific repair information should be consulted before replacing your IAC. Typical IAC replacement is as follows:

  • Disconnect the negative battery terminal
  • Disconnect the IAC electrical connector
  • Remove the IAC valve attaching screws
  • Remove the IAC assembly
  • Install in the reserve order of removal

Throttle Body Position Sensor

14. What is a throttle position sensor and what is its function in the car?

Late model engines with fuel injection use a throttle position sensor (TPS) to inform the powertrain control module (PCM) about the rate of throttle opening and throttle position. The PCM then uses this information to control various outputs such as fuel control.

15. Which are the symptoms for a broken throttle position sensor?

A faulty TPS can cause numerous problems, the most common being stumbling or hesitation upon acceleration. Usually the check engine light (CEL) is illuminated as well. Other symptoms include, but are not limited to: a change in power and response, increased emissions, an engine that runs rough and poor idle quality.

16. How can I check, if my throttle position sensor is broken?

Typically, if there is a problem with the TPS or its circuit, a diagnostic trouble code (DTC) will be stored and the check engine light (CEL) will be illuminated. If the light is on, you can plug a diagnostic scan tool into the diagnostic port under the dash and read the stored trouble codes. If the codes indicate a problem with the TPS or its circuit, a vehicle specific repair manual should be consulted for further testing.

17. How do I change the throttle position sensor?

TPS replacement varies from vehicle to vehicle, but it is fairly straightforward in most cases. Vehicle specific repair information should be consulted before replacing your TPS. Typical TPS replacement is as follows:

  1. Disconnect the negative battery terminal.
  2. Disconnect the TPS electrical connector.
  3. Remove the TPS.
  4. Install in the reserve order of removal.
  5. Adjust the TPS if required.