This is a knotty problem that started with 'bad' gas - car would drive and glide great, but cough on early acceleration which would go away with more pressure on the foot pedal.

So many fuel injector cleaners later, the shuddering problem is more pronounced, as though it is something different that the original problem.

What is this? Last week the temperature sensor was changed due to higher fuel consumption, but it didn't help the shuddering. The Mechanic's next thought is the air mass , to see if that'll help.