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The code 44 does NOT mean the o2 sensor is bad, it means there is an out of norm event at the o2 sensor, in this case lean exhaust. The usual suspect is the MAF relay and sometimes the MAF itself. Make sure the o2 wire is not melted onto the ex pipe, then when it happens again swap the 2 relays for the MAF

The usual suspect is the MAF relay and sometimes the MAF itself.
Make sure the o2 wire is not melted onto the ex pipe, then when it happens again swap the 2 relays for the MAF. One is power the other is burn-off that does not effect the run-time. If this makes a difference go buy a new MAF power relay...$7 If new relays do not do it, confirm the bad MAF with a scan or other process of elimination...MAF...$200-$350 depending on where you shop. Some used ones go cheaper and some are being rebuilt. They are expensive and do not often fail.
yeah vacuum leaks on the intake manifold, and exhaust manifold and a defective fuel injector or loose vacuum hose come to mind
This is the description of a Code 44 as set on GM products It is an indication of a lean mixture as indicated by the oxygen sensor readings.

Circuit description: The ECM supplies a voltage of about .45 volts between the appropriate terminals of the sensor. (If measured with a ten megohm DVM, this may read as low as .32 volt). The O2 sensor varies the voltage within a range of about one volt, if the exhaust is rich, down thru about .10 volt, if exhaust is lean.

The sensor is like an open circuit and produces no voltage, when it is below about 360 degrees C, 600 degreeF. An open sensor circuit, or a cold sensor, causes Open Loop operation.

Test description:

1.) Code 44 is set when the O2 sensor signal voltage remains below .3 volts for 50 seconds or more and the system is operating in "closed loop".

Diagnostic aides:

The code 44 for lean exhaust is most likely caused by one or more of the following:

1.) O2 sensor wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.

2.) Check for an intermittent ground wire between connector and sensor.

3.) Poor ECM to engine block ground.

4.) MAF Sensor - A MAF sensor that causes the ECM to sense a lower than normal airflow will cause the system to go lean. Disconnect the MAF sensor. If the lean condition is gone then replace the MAF sensor.

5.) Vacuum leaks can cause a lean condition and/or possibly a high idle. Check for cracked hoses a bad gasket or a faulty EGR or PCV Valve.

6.) fuel pressure - system will go lean, if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm.

7.) Clogged injector or lean injector - perform an injector balance test.
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