[Bigtimers227]

2011 135i 6mt n55 has 5" fmic, lwfw, stage2 clutch, bms intake, 41k miles and as of 3 days ago Cobb accessport v3...car was more modded before I purchased and had occ on and jb4 but was removed.

The issue: stock dp and as soon as Cobb went on 2 days later I'm running stage 1 aggressive fmic tune getting code P2CF4 and car is laggy power comes and goes also (smells like raw raw fuel in the cabin if the heat is on when idleing in my driveway for 30-45 mins(every now and then)). code comes back after first drive when driving hard.
On cold starts it runs rough for the first 15-40 seconds then smooths out sounds like it's missing when it's cold start for the first 15 or so sec.
O2 sensor pre cat V at idle: 1.48+/-
O2 sensor post cat V " " : 1.81 when reved drops down to 1.00 them .01+ climbs to 1.21+/- then shoots to 1.80+/-

Any input or someone that can lend a helping hand I don't know my way around the forums much but when I typed it in I dident see any stock dp issues all catless dp issues

[Bigtimers227]

Anyone?

[Sean978]

Sounds like your O2 sensor is going bad. Probably time to replace.

[Bigtimers227]

Is that the bank 1 sensor 1 o2 sensor 1-3 cylinders