Smart Forfour Check Engine + Idle Issues Fixed Here

As a Smart Fortwo owner (2015 model, gasoline), I encountered nearly identical symptoms last season. The engine stalling at idle and erratic performance pointed to air intake issues, which turned out to be more complex than initially suspected. The diagnosis revealed a significant vacuum leak where the intake hose connects to the throttle body. This was causing inconsistent manifold pressure readings, triggering the check engine light and creating unstable idle conditions. The repair required replacing the entire connection assembly due to deteriorated rubber components. The problem was serious enough to affect overall engine performance and fuel efficiency, though not immediately catastrophic. If left unaddressed, it could have led to long-term engine damage due to improper air-fuel mixture. Key indicators to watch for during diagnosis: Irregular idle speed fluctuations, Whistling sound near the throttle body, Reduced engine performance under load, Changes in engine sound when manipulating the throttle A proper inspection should include pressure testing of the entire air intake system and thorough examination of all connection points. Getting this diagnosed correctly is crucial, as misdiagnosis often leads to unnecessary parts replacement.

Thanks for sharing your experience. That sounds exactly like what I am dealing with, especially the whistling noise and unstable idle. My check engine light has been persistent too. I am planning to have the vacuum hoses and manifold pressure system checked thoroughly at a different shop this time. The symptoms you described with the air intake match perfectly with what I am experiencing. Would you mind sharing how much the repair ended up costing in your case? Also curious if you have had any related issues pop up since the fix?

After having the repairs done, I can confirm the air valve issue was completely resolved. The main problem turned out to be a faulty hose connection from the pump to the valve, which was causing those unstable idle problems and the annoying whistling noise. Total cost came to 175€ for parts and labor. Since fixing the manifold pressure system, the check engine light has stayed off and the engine runs smoothly. No more engine stalling or irregular idle speeds. The air supply system now works perfectly, and I have not experienced any related issues in the months following the repair. The investment was worth it to resolve the problem properly. The symptoms you are describing sound identical to what I experienced, so having a thorough inspection of the entire air intake system would be a smart move.

Thanks to everyone for the helpful advice. I finally had my Smart Forfour checked at a new repair shop and wanted to share the outcome. The mechanic found multiple vacuum hoses that had deteriorated, causing significant vacuum leaks in the air supply system. The check engine light was triggered by inconsistent air pressure readings, just as suggested. They performed a complete pressure test and replaced all the compromised hoses. Total repair cost was 220€, which included new hoses, gaskets, and labor. The engine now idles perfectly with no whistling sounds. The repair shop also cleaned the throttle body while they were working on it, which helped improve overall performance. It has been two weeks since the fix, and I have not experienced any engine stalling or irregular idle issues. The check engine light has stayed off, and the car runs better than it has in months. Definitely worth getting a second opinion from a different mechanic.