Vehicle year/make/model/mileage would help.
However, check the following:
1. Oxygen sensor.
2. PCM Grounds.
3. Fuel pressure. This is not likely the case because it could also set a
P0137 DTC if the pressure is too low.
4. Perform injector balance test.
5. Check for vacuum leaks.
6. Check for exhaust leaks.
7. MAF sensor. Disconnect and see if problem goes away, if so, replace MAF
8. Fuel contamination (water)
9. PCM connections.
10. Wiring harness.
11. Secondary Air Injection Reaction (AIR) system for damage or leaks,
especially check valve.
12. PCV Valve and associated hoses.
This is where a scan tool rather than a code reader would come in handy.
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