Smart Forfour MAF Issues Cause Stalling and Heavy Smoke

I had a very similar situation with my 2007 Smart Fortwo diesel last year. Having some experience with basic maintenance, I initially thought it might be a dirty air filter causing the performance decline. The symptoms matched yours exactly, unusual engine stalling, increased fuel consumption, and visible smoke. The air-fuel ratio was clearly off, causing these issues. After checking the air filter and finding it clean, I took it to my regular workshop. The diagnostic test confirmed a faulty MAF sensor. They explained how this sensor measures incoming air flow and sends data to the engine control unit. When it fails, it causes incorrect air-fuel mixture calculations. The repair included: Complete diagnosis, MAF sensor replacement, System reset, Test drive to confirm fix Total cost was 365€ including parts and labor. After the repair, all symptoms disappeared and fuel economy returned to normal. To help further with your case, could you share: Current mileage, When the symptoms first appeared, Whether the symptoms occur more during cold or warm engine, Any recent maintenance performed, Any engine codes showing This information would help determine if your situation is indeed similar to what I experienced.

Thanks to all replies. The issue occurred just after reaching 182304KM. Recent full service was 6 weeks ago, and symptoms started appearing gradually over the last 2 weeks. The check engine light started flashing only when the engine is warm, especially during acceleration. The MAF sensor failure symptoms match perfectly, the stalling and smoke are most noticeable after 10-15 minutes of driving. Based on the suggested fix and cost breakdown, I will book an appointment to have the mass air flow sensor replaced. The performance decline matches the pattern others described, and given the mileage, a sensor failure seems the likely culprit. The quoted 365€ repair cost seems reasonable if it resolves all these issues.

I am glad to hear back about your situation. The timing of your symptoms, appearing after 182000km and getting worse when warm, matches exactly what I experienced with my Smart. Just like your case, my check engine light also started acting up mainly during warm operation. The gradual onset of issues over weeks is another typical sign of MAF sensor degradation that I noticed in my car. The air-fuel ratio becomes increasingly incorrect as the sensor continues to fail. Since your recent service was only 6 weeks ago, and they likely checked the air filter then, it reinforces that the MAF sensor is the likely culprit. The engine stalling and smoke patterns you describe mirror what I dealt with before replacing mine. One tip from my experience: Make sure they clear all engine codes after installing the new sensor. My workshop had to perform this additional step to get everything working properly. The 365€ cost is standard for this repair based on current parts prices. In my case, the investment was worth it, the car has been running perfectly for over a year now with no performance decline or engine stalling issues.

Based on all the input received, I have decided to proceed with the MAF sensor replacement. The symptoms align too perfectly to ignore, the stalling after warm-up, increased fuel consumption, and smoke during acceleration. The timing of these issues after 182000km also matches what others experienced. The check engine light behavior during warm operation seems to be a common pattern with mass air flow sensor failures. Since my recent service checked all other potential causes, this appears to be the most logical fix. I will schedule the repair next week and ensure they perform a complete system reset after installing the new sensor. The 365€ total cost seems reasonable given the parts and labor involved, especially if it resolves all these performance decline issues. Will update the forum after the repair to confirm if this fixed all the problems. Based on others experiences with similar symptoms, I am confident this will resolve the engine stalling and fuel economy issues.