Car will not start when Mass Air Flow sensor is plugged in; when it is unplugged the car will idle and gradually idle up if you give it very little fuel at a time. Installed a used Mass Air Flow sensor and nothing changed. Any ideas.

DTC P0121: Throttle Position (TP) Sensor 1 Performance
Circuit/System Description
The engine control module (ECM) uses the following information to calculate an expected airflow rate:
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The throttle position (TP)

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The barometric pressure (BARO)

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The manifold absolute pressure (MAP)

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The intake air temperature (IAT)

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The engine RPM

P0121 The predicted air flow and the predicted MAP combined are outside a calibrated range for more than 3 seconds.
Circuit/System Testing

1. Inspect for the following conditions:
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Vacuum hoses for splits, kinks, and proper connections as shown on Vehicle Emission Control Information label



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Inspect thoroughly for any type of leak or restriction



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Air leaks at throttle body mounting area and intake manifold sealing surfaces



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Throttle body for dirt, debris, and coking--Refer to Throttle Body Cleaning.


2. Allow the engine to reach operating temperature. Observe the MAP Sensor Voltage parameter with a scan tool. Voltage should be more than 0.8 volt and less than 4 volts.
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If more than 4 volts or less than 0.8 volt, refer to DTC P0106.

3. Idle the engine. Observe the MAP Sensor kPa parameter with a scan tool. Increase the engine speed slowly and then back to idle. The MAP sensor kPa should change smoothly and gradually as engine speed is increased and returned to idle.
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If the MAP sensor kPa does not change, refer to DTC P0106.

4. Take a snapshot of the engine data list while performing the actions listed below. The mass air flow (MAF) sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.
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Idle the engine.



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Increase the engine speed slowly to 3,000 RPM, then back to idle.



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Exit from the snapshot and review the data.



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Observe the Mass Air Flow (MAF) Sensor parameter frame by frame with a scan tool. The MAF sensor g/s should change smoothly and gradually as the engine speed is increased and is returned to idle.



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If the MAF sensor g/s does not change smoothly and gradually as the engine speed is increased and is returned to idle, refer to DTC P0101 or P1101.


5. Inspect the throttle body for the following conditions:

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Loose or damaged throttle blade

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Broken throttle shaft

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Any throttle body damage

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If any of these conditions exist, replace the throttle body assembly.

Had a similar problem that I was able to solve with an intake manifold cleaning as

may be it was not the MAF sensor but bad connections in the wires. Have a technician check the voltage in the wires and connectors to determine if that was the fault to start with

This is a symptom of a bad mass air flow sensor. This is the sensor in line between the air filter and throttle body. Unplug it and see if it idles. If it does replace it.

this vehicle most likely has a mass air flow sensor it may have got accidently unplugged or the air tube from mass airflow to engine is not connected well or it could be that you have indeed a bad mass air flow sensor they do make a special cleaner that you may want to try before purchasing a mass air flow sensor or purchasing one from salvage yard the symptoms you describe would be created by a bad massair flowsensor

Running rough?? If i took a guess I'd say there's a faulty injector. Does it smoke like hell ?? Does it also miss at idle?- If so get a line wrench and a rag handy. Start the car and while idling wrap the rag around the base of the fuel line connector on injector 1 and crack it just a bit until fuel comes out. It might spray, thus the rag. If the miss gets worse, that ain't the injector to blame. Continue with the other 3. If you crack a line and there is no or very little change in the miss then you found the guilty party.

On a long shot it could also be a stuck valve.

Did that get it?? It sounds like an issue other than MAF but.... get a multimeter and try probing the connecter to the MAF. When you find out what it is , please let me know. I'm curious

*The key must be on*

pin 1- ignore it
pin 2- gnd = 12-14v
pins 2- 3 = 12-14v
pin 4- gnd = 5v
pins 3- 4 = 5v

P0101 - Mass Air Flow Sensor (G70): Implausible Signal

Possible Symptoms

• Loss of Power
• Erratic Idle

Possible Causes

• Mass Air Flow Sensor (G70) faulty
• Air Leak(s) after Mass Air Flow Sensor (G70)
• Intake Air Filter dirty/faulty
• Ground Spots corroded or Paint Residue
• Wiring and/or Connections from/to Mass Air Flow Sensor (G70) faulty

Possible Solutions

• Check Intake Air Filter
• Check Mass Air Flow Sensor (G70)
• Check Ground Spots
• Check Wiring and/or Connections from/to Mass Air Flow Sensor (G70)

You need more information. I would start looking for a vacuum leak, especially if the mass air flow sensor is still not giving the desired readings. The O2 sensors will likely also be off.

Check the fuel pressure. If good, then see if there is vacuum leak with a vacuum gauge. If good take the idle control valve off and see if there is a lot of grim inside. Or it may be the mass air flow meter maybe bad. Try cleaning it with some mass air flow cleaner. See if it idles better with intake cleaner being sprayed in the intake with it running. First see if it runs a little better with the mass air flow unplugged. If so then the sensor is bad.

sounds like mass air flow sensor on the intake system needs changing. check for vacuum leaks, make sure car has normal tune up done

I suspect you have an idle circuit issue. When the thottle is closed, the throttle valve is almost closed (like 95%). The linkage on the throttle body is against the hard stop.
SO, when idling you need a way to let enough air into the engine to maintain an idle speed. The IAC, Idle Air Control valve is the way you do that and the engine computer controls the rate of air flow.
Sometimes it gets plugged up so you can clean it with a little carb cleaner. Might have to take it apart.
Also, you have a MAF, Mass Air Flow sensor that tells the computer how much air is flowing through the air cleaner intake at any time. The sensor gets coated with varnish and vies a false reading. Clean it gently with carb cleaner and a toothbrush.
Other than that, I would go to an auto parts store that can run a computer scan for free to see if you have any fault codes stored. They will tell you next stpes.

I assume you 2.0L SPI engine & not Zetec.


Idle Air Control (IAC) Valve —2.0L SPI Removal

1. Disconnect the idle air control (IAC) valve electrical connector (air cleaner outlet tube removed for clarity).

1. Remove the IAC valve.

1. Remove and discard the IAC valve gasket.

Mass Air Flow (MAF) Sensor Removal

1. Remove the air cleaner outlet pipe.

1. Disconnect the mass air flow (MAF) sensor electrical connector.

1. Remove the MAF sensor.

clean element inside carefully


PS. A good running engine makes for a better running transmission