You need to calibrate your meter to the 50% duty cycle that comes with the O2 sensor disconnected.

If you aren't reading 50% then your tool is set-up wrong (or defective). Or you have a lambda system problem.

You need a baseline when doing testing. It is my guess you are reading wrong and that is why things don't work right.

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