Smart Roadster VANOS Fault Causing MPG Drop & CEL

Recently had similar issues on my 2008 Smart ForTwo Coupe. The check engine light came on repeatedly and the engine showed rough idle symptoms. After proper diagnosis, it turned out the variable timing system was malfunctioning due to a failing VANOS solenoid. The symptoms matched yours, poor fuel economy and inconsistent engine performance. The repair involved replacing both inlet VANOS solenoid and cleaning the related components. This is actually a common issue on these engines when they reach higher mileage. The repair was significant but not catastrophic. The important part is addressing it promptly since a faulty VANOS solenoid can lead to engine misfire and potential long-term damage to the timing components. The complete job took about 4-5 hours at the shop. Would suggest getting the error codes read first to confirm the VANOS fault. If confirmed, better to replace the solenoid rather than attempt cleaning, as these parts typically degrade over time and cleaning provides only temporary relief. Key warning signs that confirmed the diagnosis: Rough idle, Decreased power output, Check engine light, Worsening fuel consumption, Slight ticking noise from valve cover area

Thanks for sharing your experience, that really helps. My Smart Roadster ended up having the exact same VANOS solenoid failure symptoms you described. Got it fixed last month and the low power issues disappeared completely. The engine feels much smoother now, especially at idle. Just curious, do you remember how much you paid for the complete repair? Also, has everything been running smoothly since the fix? My mechanic mentioned something about checking the inlet camshaft in 6 months just to be safe.

The VANOS repair on my ForTwo cost 250€ total, which covered replacing the faulty inlet camshaft solenoid valve. This price was reasonable considering the technical nature of the work. Running perfectly since the fix, no more engine misfire issues or rough idle problems. The improved engine response and power delivery really shows how much the faulty VANOS was affecting performance. Fuel economy is back to normal too. Good call by your mechanic about checking the inlet camshaft later. While the VANOS repair typically resolves the timing chain and power delivery issues completely, a follow-up inspection can catch any potential wear patterns early. Since getting the defective solenoid replaced, I haven't needed any additional work on the VANOS system. A properly functioning VANOS makes a huge difference in how these engines run. The smooth idle you're experiencing now is exactly what you should expect when everything is working correctly.

Thanks for the input. Wanted to share how my repair went. Took the car to a specialist shop after getting those concerning symptoms. The mechanic found significant oil sludge buildup around the VANOS unit during inspection, which explained the variable timing issues I was experiencing. Final repair bill came to 380€ including parts and labor. They replaced the inlet VANOS solenoid and did a thorough cleaning of the surrounding components. The difference in performance is remarkable, no more low power issues and the engine runs smoother than it has in years. The entire job took about 6 hours since they had to deal with some stubborn buildup. Really glad I addressed this before it caused more serious engine damage. Will definitely get that follow-up inspection in 6 months to ensure everything stays in good shape. The fuel economy has improved significantly too, getting about 15% better mileage now that the timing system is working properly. Should have done this repair months ago when the symptoms first appeared.