If it wonders around it actually sounds more like it got loose and is too close to something hot. Does it seem close to ambient at cold start?

To test my theory, take some "canned air" and spray it upside down into the port where you can get the spray to vaporize close to the sensor.

It's important there is no air path from the hot radiator to the sensor. Maybe stuff some foam or insulation to make sure there is no hear soak from the radiator output.

Case in point: I've seen readings 40°F higher then ambient on my M54 when not moving and hot air from radiator works into the duct.

Is it possible you are just getting a path of hot air where it shouldn't be?

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)