High LTFT (Over 30%) - MBWorld.org Forums

Yesterday | 02:49 PM

fxx

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Joined: May 2026

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From: Brazil

C180 Coupe Sport 2019

High LTFT (Over 30%)

Hello,

I have a 2019 Mercedes C180 W205 and I've been fighting high fuel trims for over a month.

The issue started after a 400 km trip where the car entered limp mode with a cylinder 1 misfire. Spark plugs were replaced and the misfire never returned.

Later I noticed:

LTFT around +25% to +45%
P2177 lean code
car felt heavy/sluggish
battery voltage was very high (14.8–15.1V)

I replaced the battery and idle became smoother, no much vibration, and lower map values on idle.

I also noticed the pre-cat O2 sensor (O2S1) was barely reacting, so I replaced it. After that:

car became much smoother
P2177 never returned
STFT behavior became much more normal

I also had these codes before changing the battery:

P007D (intercooler temp sensor circuit high)
P0238 (boost pressure sensor high input)
P1190 (Intake Air Pressure Sensor Fault)

Because of that, I replaced the MAP/TMAP sensor too this weekend.

Now

no limp mode
boost feels smooth and linear
car drives much better overall

However, LTFT still stays high around +28% to +32%.

I already reset fuel trims around 5 times and even disconnected the battery for over 1 hour, but trims always come back high after driving.

Additional info:

O2S1 now oscillates normally
MAP idle = 4.5 psi - 5psi - and it gos up to 31 psi on WOT(total)
O2S2 stays around 0.7V
STFT is usually close to 0% when driving
- STFT negative on idle (-10 to zero)
- STFT negative in some pulls (-2, -3)
- STFT positive in some hard pulls (7-8 intant then downs to 3-0)
- STFT positive in high gear around 80kmh but not always
fuel economy is around 7 km/l city and 15–17 km/l highway (for city is not good and car feels like heavy)

At this point I'm trying to understand: