Modern Vespa

2019 Primavera 150. Hey everyone, I bought a pair of Primavera brand new 2019 150's around April of 2020. I rode one of them primarily and racked up 4500 miles on it and needed to change the tire. I dd this work myself and I had to remove the muffler to remove the tire. I got the new tire back on and reinstalled the muffler and now the check engine light comes on within a out 30 minutes of riding... also, I get a little sputtering and even a stall out now and then.

I decided to change the spark plug hoping that was the problem. The spark plug was black and burnt looking so I felt like I discovered (and fixed) the problem. Unfortunately I did not. The light still comes on and I still get a little sputtering from the engine..

Is it possible the O2 sensor is bad? Would that make the spark plug get black and cause some sputtering??

I had to unplug the sensor when changing the tire so this is my best guess.

Thanks in Advance fir any help!

Possibly the exhaust bushing is damaged