Question Details

Hello. I'm working on a Mercedes w203 Kompressor with a 1.8L I4 Turbo engine. I was called in to solve a misfire on warm-up. By the time I got there coils and plugs were swapped but the car still ran badly. I found misfire codes for all cylinders and o2 B1S2 heater. I suspected the misfire codes were due to mechanic unplugging coils. So I cleared them and they didn't return but the o2 heater did.

I discovered that when the car is running badly it won't enter closed loop, STFT stays 0.0, LTFT 14.1 and B1S1 o2 is 2.3 +/- 0.1. At this time the fuel trim will not adjust to forced lean, pulling vac line, or forced rich, adding carb spray. The car runs just fine when the B1S1 is
@ 1.5 (normal fluctuations). It'll enter closed loop, fuel trim will adjust LTFT is fixed @ 14.1 and STFT was high pointing me to find the broken vac brake booster line fitting causing lean condition.

Anyone ever met this issue with a car not going into closed loop intermittently? I'm thinking Upstream o2 going crazy or bad ECM.