The values you are seeing are near the end of compensation especially the 12.6 number.

You should do some standardized testing. Check the numbers at various rpms and always at constant speed. If you are getting closed loop activity at around zero at some point you need to know what about the new point has changed. If you increase speed and loose control you may need to see the differential pressure. The 12.6 number has lost control. (Control is the back and forth change of the current value. If the number just keeps getting bigger or smaller it is not in control.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician