[ch1nczyk]

Reaching out seeking some guidance on diagnosing the increased fuel consumption on my 2007 E90 328i N52B30 with 160k km (100k miles) on it. The fuel consumption is currently at 15.6l/100km (15 mpg), and for the last 100k kilometers, it was fixed at 13.3l/100km (17.7 mpg), which I think is close to what other owners are reporting.

Backstory:
Around February this year, a faulty little heater (this one: 11617561408) has malfunctioned, to the point where it started melting (?) and producing smoke. This has caused the electric breaker to go-off, resulting in all Lambdas also going offline (check engine soon etc). The engine would run normal but with heavily increased fuel consumption during that time - I guess this is to be expected with no Lambdas.

A couple of weeks later (3-4) the breaker and angle valve were fixed and the check engine disappeared. The car back then, as well as now, would report absolutely no DTC errors whatsoever.

The fuel consumption however increased by around 17% (2.3l/100km) and does not want to get any lower; my driving profile is the same all the time, mostly in the city.

I did analyze it with the Bimmerlink to get the readings of the Lambda sensors, MAF, coolant temp, Open/Closed loop, ST/LT Fuel trims - things tend to look normal, I'll paste some of the values here but do let me know if you want to have anything specific as I may also have checked it

Coolant temp: 98-100*C (208-212F)
MAF: 2-4g/s on idle, up to 12-14g/s on around 2500 RPM
ST Fuel trims: circulating around -5/+5%
LT Fuel trims: bank 1 and bank 2 differ, with bank 1 being always lower at around 0-5%, and bank 2 being at 5%-12%, both noticeably increase at idle.
Lambda Sensors 1 (bank 1 and 2) - at fixed 2.0V when idle, circulating between 1.5V (heavy load) - 3.2V (downhill ride with throttle off)
Lambda Sensors 2 (bank 1 and 2) - fixed 0.6-0.8V, generally not responding to throttle, but noticed they go down to 0.0V on downhill ride (when sensors 1 are at 3.2V).

The engine otherwise runs pristine - doesn't shake, constant RPM, no loss of power, and no other error codes.

Does this ring a bell to anyone? Should I maybe reset (and how) the ST/LT trims after Lambdas went offline for several weeks? What else can I diagnose to get to the bottom of the problem?

Any pointers & help is greatly appreciated!