A sensor was replaced in the automatic transmission of my 2013 Subaru Legacy recently. Since then, the car has had the following intermittent problem:
Periodically, the car will shudder briefly, or sometimes for several seconds. As far as I can tell, this occurs only at about 1500 rpm, which I associate with a gear change. It can happen across a wide range of speeds.
It does not always happen; I can drive it for a long time without seeing this behavior, while my son often has it happen to him (also if I am in the car as a passenger).
Testing conditions: if you reduce pressure on the accelerator just as the car is switching gears, the shuddering is very likely to kick in. But it has apparently also happened at higher speeds on the highway with cruise control on: then the shuddering keeps happening for a while.
It only happens when accelerating, not when decelerating. It does not happen when the engine is very cold. It does not happen if you accelerate through a gear change.
I am wondering if the reduction in gas just after the transmission shifts into a higher gear is causing some problems. I believe this can be a problem for manual transmissions; can it also be the case for automatics?