Hello fellow Miatans : )
I'll try to make the story short, and yes, I've searched and did some homework.

For the last 6 years, I'm driving a manual 2005 NB, the sports suspension version.

Lately, I'm getting the P1170 (front O2 sensor, high voltage) CEL.
It usually lights up at high speeds, about 140 km/h.

What I've recently changed/fixed:
-catalytic converter + 2 new O2 sensors
(had coils-related ignition problems about a year ago, so the converter died..)
-new Air and Fuel filters.
-cleaned the MAF (not thoroughly)
-checked and cleaned O2 sensor contacts
-didn't help, and additionally, the coils started to fail - had bad Chinese coils unfortunately, that broke apart inside the engine : (
(what's weird, is that even though the engine was misfiring - didn't get the appropriate CEL)
-yesterday, installed a set of new good plugs and coils
-today, the CEL is back on!

Symptoms:
-low MPG (about 1L/8km, instead of 1/10 - my "regular" driving MPG)
-sometimes, misbehavior at idle: +/- 100/200 RPM
-before changing the coils - hesitant throttle response (gone now)
-before changing the converter and fuel filter (which was dirty as hell) - the car felt "weaker" by about 10-15%

-hopefully not related, but what if(??):
weird, inconsistent electrical buzzing noises, that come and go as they please, from the relays location at the drivers left knee, under the wheel.

Planning:
-inspect and clean (again) the front O2 wires
-clean the MAF thoroughly with the BG cleaner
-clean the throttle body
-install new ignition wires (should arrive this week)
-add BG 44K injector cleaner
-clean all the relays, to hopefully, eliminate the buzzing

Any other suggestions will be highly appreciated!!
I'm about to install a FF supercharger, and must solve this problem ASAP.

thanks,
Daniel.