2011 mb c300 sport - sluggish/vibration upon acceleration

What is your question?

Intermittently, especially going uphill or from stop to start. After that, it runs smooth and seems it has normal power. Sounds like it is idling fine at 600 rpm. I thought the 5 year old spark plugs were the cause. Changed them. Same condition. Added some Gumout fuel injector cleaner to 12 gallons of gas. No improvement. Car just passed SMOG test. No faults.

What makes this problem better or worse?

Going uphill or starting from a stop

How long has your 2011 Mercedes-Benz C300 had this problem?

months