Bosch HFM5 burn-off procedure?

[subwoofer]

It seems I am contaminating my MAF, flow estimation keeps creeping lower over time, a good cleaning with CRC Air Sensor Clean seems to restore calibration. It seems to be needed every 6 months or so, after that EGO runs out of authority. The suspected cause is engine oil mist, the engine is due for replacement soon.

I have heard rumors that the Bosch Motronic ECUs "burn off" the MAF after running, does anyone have any details on how this is done? Is it simply a matter of keeping it powered for a few minutes after shutdown?

[elaw]

The HFM5 doesn't have a burn-off function.

With the older Bosch sensors (that used a platinum wire instead of a hot film element), there's a dedicated pin for that function. A couple of seconds after the car was shut off, the ECU would apply +12 to that pin for 2 or 3 seconds to effect the burn-off. I think the pin was actually connected directly to the sensing wire.

How are you getting oil mist on your sensor? The sensor is supposed to be located upstream of any source of contamination so that cannot happen.

[subwoofer]

Before I moved it last year, it was sitting 2-3" upstream of the crankcase breather port, that caused oil contamination. I have since moved the MAF about 2' away from the port, it now sits right at the (Chinese K&N knock-off) air filter. Contamination would come from suspended droplets traveling backwards after stopping, I am guessing here.

I have not yet fully investigated the matter this time, car is still full of holiday luggage and the engine bay hatch is buried beneath it. Will disassemble on Sunday, after the car is emptied. I just noticed two days ago that I ran out of EGO authority.

[elaw]

Can I make a suggestion? Replace the air filter with a good paper one and see what happens.

I know there's some argument about this, but I've seen a lot of things indicating K&Ns (and presumably the knockoffs) don't do a very good job of filtering the air. I suspect it may not be oil but small particles in the air that are making your sensor unhappy.

[subwoofer]

Will see if I can find and fit a suitable air filter box, after a few other items are checked out. If cleaning it doesn't help, air leaks, fuel pump (24 years old, presumably) and FPR (same age) are the next suspects.

I don't disagree with your thoughts on paper filters, the K&N style was fitted due to convenience.

[subwoofer]

Sensor cleaned and restored to working order. The film surface looked a little flat, running a Q-tip onto it revealed a blackish contamination. No part of the sensor looked like it had oil on it.
The problem may well be dust coming through the air cleaner, I will have to look into a better solution.