Mileage 232,790. Changed timing belt for the 2nd time about 2 months ago. Since the timing belt service, I notice a vibration or trembling that occurs only on acceleration. That is, if the car is standing still in park or neutral and I rev the engine there is absolutely no vibration.

Scenarios:
a) Driving at low speeds and not accelerating, e.g. in traffic - no vibration.
b) City driving (low speed) but accelerating as if taking off from a traffic light - trembling occurs
c) Driving at highway speeds and not accelerating (e.g.in cruise) no vibration.
d) Coming down a slight grade at highway speeds with foot off the gas, likewise no vibration.
e) Highway driving but having to give her gas when going up a slight grade, she trembles.

Trembling can be felt in the steering wheel and even by another passenger. It's like driving across a grating or as if the road had tiny grooves across it. I took it back to the shop and they said they test drove it under different conditions and could not replicate.

I just drove 390 miles today and could feel it each time. I am convinced it is not speed-related. Also, she was as smooth as silk prior to the timing belt service. Could it be faulty components?

Help!

 

Try a new set of plugs and coils.