Smart Fortwo Diesel Stalling Fix: Check IAC Valve First

Had a similar issue with a Smart ForFour CDI from 2005. The engine idle was unstable, dropping RPMs and stalling, especially when the engine was cold. The root cause was severe carbon buildup in the air intake system and throttle body. The IAC valve was completely clogged, preventing proper air flow regulation during idle. An inspection revealed the throttle body was also heavily contaminated, restricting proper air passage. This required thorough cleaning of the entire intake system, replacement of the IAC valve, and recalibration of the idle control system. Not a simple DIY job, needed specialized cleaning equipment and diagnostic tools to reset the system properly. This is actually a serious issue that needs immediate attention. Running the engine with a malfunctioning air intake system can lead to: Poor fuel economy, Increased emissions, Additional engine damage, Complete stalling in traffic The symptoms you describe match exactly what happened in my case. The check engine light indicates the ECU has detected irregular air-fuel mixture readings, which is consistent with a clogged IAC valve or contaminated throttle body. Recommend getting it checked professionally rather than attempting quick fixes, as proper diagnosis and cleaning are essential for long-term resolution.

Thanks for sharing your experience. The same problem happened with my Smart Fortwo last winter, irregular engine idle and stalling issues. The IAC valve was indeed the culprit, along with a dirty throttle body. The stalling engine symptoms cleared up completely after the fix. Just wondering, do you remember the total repair cost for your IAC valve replacement and system cleaning? Also, has your idle speed remained stable since the repair, or have you noticed any other problems? This seems to be a common issue with these models when they reach higher mileage, and its good to know the typical cost range for future reference.

After getting the mechanic to fix both the faulty air valve and clean out the contaminated intake system, my Smart runs perfectly now. The total repair came to 425€, which included replacing the bad idle air control valve and a deep clean of the severely blocked intake components. Since having that work done about 8 months ago, the engine idle has been completely stable with no stalling issues whatsoever. No other problems have come up either, the engine runs smoothly whether cold or warm. The price was worth it considering how much smoother the car runs now. The mechanic mentioned this is a maintenance item they see regularly on these models. Regular cleaning of the air intake system can help prevent complete IAC valve failure and keep the idle stable for longer. The stalling engine symptoms disappeared right after the repair. Make sure to get a full system cleaning done along with the valve replacement, just swapping the IAC valve alone wont fix the underlying contamination causing the problems.

Glad to report back on my mechanic visit! After seeing all the helpful replies, I took my Smart in last week. The mechanic confirmed the engine stalling was indeed from a faulty IAC valve and dirty throttle body, just as suspected. The total bill came to 380€ for cleaning the entire air intake system and replacing the air valve. Initially thought it was steep, but watching the mechanic work showed just how gunked up everything was. The car idle is now perfectly smooth, no more stalling or rough running. The repair took about 3 hours total. Had them do a basic inspection while they were at it, and everything else checked out fine. The engine runs like new now, especially at idle speed. Best part is the check engine light finally went off. For anyone else facing similar symptoms, definitely worth getting it checked out promptly. Letting these issues go can apparently cause bigger problems down the line. Very happy I got it sorted before winter hits.