2012 Equinox 2.4L Rough Idle in Reverse

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twenzel

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Hello,

2012 Chevy Equinox with 80,000 miles on chassis and 5,000 on rebuilt engine from a reputable, national builder. Engine was replaced due to excessive oil consumption.

About 8 months after engine replacement, the 2.4 started to idle terribly when cold started and shifted to reverse.

Relevant facts:
  1. Does NOT set a code
  2. Does NOT set a mis-fire
  3. LT Fuel Trim at -3 after running
  4. ST Fuel Trim oscillates between -5 to +2
    1. Seldomly to Plus side
    2. Does seem to be quite active and all over the board
  5. Throttle Position responsive and in spec
  6. Cylinder Balance in spec
  7. Injector pulse in spec
  8. Engine Mounts good
  9. Battery replaced
  10. MAP replaced
  11. Traced each connection wire status through the loom
  12. Checked pins of each connector
  13. Vacuum leak checks down to the intake manifold with NO vacuum leak
  14. Nothing from the Fuel Trim indicates a rich condition
  15. Ran system without EVAP to test for symptom - with EVAP blocked off, symptom persisted
  16. Tests and system monitor through Snap On Solus Scan Tool

New Parts installed during Engine replacement
  1. Plugs
  2. Cam Phasers
  3. VVT sensor
  4. Coolant Sensor
  5. Thermostat

Watching bank 1 O2 sensor is active and seems in range. I have not replaced the O2 sensor as it appears functional.

I have never seen an ECM replacement solve a situation like this, but we are at wits end here....

General Thoughts on Progression:
  1. Potentially replace high pressure fuel pump
  2. Potentially replace primary O2 sensor
  3. Potentially replace ECM
  4. Potentially replace High Pressure Fuel pump
  5. Could swap out Cam solenoids; but they are active and within spec
  6. Thought about a torque converter issue, but if the engine is not running correctly, the tranny will not function properly....and vice versa

At this point, we are leaning towards replacement of the High Pressure Fuel Pump. Any thoughts? Running out of money and patience

Condition seems to go away after the vehicle has warmed up.

Thanks in advance
 
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