Year: 2005, Make: Toyota, Model: Vitz, Odometer reading: Over 100K, Transmission: Automatic, 3 cylinder engine. 

This car had the craziest of vibrations. The engine would shake so much especially when you stopped with your foot on the brakes and with the transmission on D at a traffic stop. I would just put it on N. But recently it even vibrated on N. 

I tried everything. Changed plugs, all mounts, crank shaft pulley (which was worn) and the belt. Sometimes it would reduce the vibrations, but nothing really worked. The engine would vibrate as if it wanted to fly. Many mechanics said it's just characteristic of 3 cylinder engines. 

The last thing I was planning to do was to do an overhaul of the engine and sell it if that didn't work. 

Luckily, after 2 years, a mechanic who was fixing something else on the car, suggested we clean the throttle body. He took it out, used some WD-40 to clean out some dirt. And voila, the vibrations are GONE. Completely gone. The three cylinder vibration theory debunked. 

Just sharing in case it might help someone. 

Vusile - Tanzania