Smart Fortwo Mount Failure Causes Rough Engine Idle

Had similar symptoms on a 2009 Smart ForFour with the 1.1L engine. The rough idle turned out to be a combination of motor mount wear and a damaged wiring harness connector near the engine mounting bracket. The mount failure was obvious once the car was lifted, the rubber had completely separated from the metal housing. The vibration was transmitting straight through to the chassis, causing that harsh shake at idle. The damaged wiring harness was making intermittent contact, triggering fault codes. The complete repair required: Replacing two engine mounts, Rewiring the damaged connector section, Clearing fault codes, Testing mount alignment This was not a quick fix, took two full days at the shop. Mount wear is actually a common issue on these engines, especially when the car sits for long periods. The electrical connection problem made diagnosis trickier since it presented similar symptoms. Key warning signs to watch for: Clunking noise when shifting gears, Excessive engine movement, Vibration through steering wheel, Progressive worsening of idle quality Recommend having all mounting brackets inspected while the work is being done. The electrical connections near the mounts should also be checked for damage from excess movement.

Thanks for sharing your experience. I had nearly identical mount failure symptoms on my Smart Fortwo last year. The vibration issues were getting worse each week until it became unbearable at idle. Did you experience any additional problems after the repair was completed? Just want to make sure Im prepared if anything else needs attention. Also curious about the total repair cost in your case, would help me budget properly since Im planning to get this fixed next month. The engine mount wear on these cars seems pretty common from what Ive researched in forums, but Id like to know if your fix has held up well.

Since getting the Smart ForFour fixed, the motor mount repair has held up perfectly with no recurring vibration issues. The defective engine mount was causing most of the problems, but the real culprit was actually a loose cable connection near the mounting bracket. The total repair came to just 95€ for fixing the faulty wiring, much less than expected since no physical mount replacement was needed. The mechanic found the failed mount symptoms were triggered by the electrical fault, not actual mount wear. The idle is now completely smooth with no more fault codes appearing. A proper diagnosis really made the difference, what seemed like serious engine mount problems turned out to be a relatively simple electrical fix. Worth having a thorough inspection done to rule out similar connection issues in your case before replacing mounts. If the engine does show signs of physical mount wear, getting all mounting points checked is recommended since they tend to deteriorate at similar rates. But start with the electrical connections since that can mimic mount failure symptoms as I discovered.

I finally took my Smart Fortwo to a mechanic after dealing with those mount failure symptoms. The vibration was getting worse every day, making the car almost undriveable at idle. Turns out both the transmission mount and motor mount were completely worn out. The rubber mount material had degraded badly, causing that harsh vibration. The mechanic found metal-on-metal contact where the mounts had failed. The repair took about 4 hours total. They replaced: Both engine mounts, One transmission mount, Cleaned all mounting brackets, Reset the fault codes Total cost came to 485€ including parts and labor. More than I wanted to spend, but the car runs perfectly smooth now. No more vibration or clunking when shifting. The idle is stable and all fault codes are cleared. Really glad I got it fixed, the mount wear was much worse than expected and could have caused more damage if left unchecked. The mechanic did a thorough job checking all mounting points and connections. Money well spent to solve the problem properly.