My 2011 Impreza has acceleration hesitation issues if RPM is below 2K. Once it reaches 2K, problem goes away but comes back again when it upshifts and RPM falls below 2K. I've tried cleaning the MAF sensor and relearn throttle position but problem still persists. Any suggestion what to do next?

scan for trouble codes .

if knock sensors go bad they can cause loss of power without always throwing a check engine light.

Lack of power on early FB's is very likely to be broken valve springs. There is a recall. Take it to the dealer to be checked out. 

.....if it has an FB. Forester did in 11, but I might be a year off on the Imp. 

GD

Edited January 24, 20197 yr by GeneralDisorder

yikes

"The recall for the valve spring issues, involves vehicles manufactured from January 16, 2012 to May 14, 2013. The affected models are 2013 Model Year (MY) BRZ, 2013-2014MY Legacy/Outback, 2012-2014MY Forester and 2012-2014MY Impreza/XV equipped with the FA20 engine or FB20 engine."

Mine is a 2011. Will have it checked tomorrow..

Hhhhmm yeah I don't understand why the 11 Forester isn't listed because that absolutely is an FB25. But maybe it was a supplier thing only affecting 12 to 14. 

GD