I just had the headgasket replaced on my 2010 Outback. They also replaced the water pump, timing belt, and resurfaced the heads. It doesn't overheat anymore, but the passenger compartment smells like gas and it idles rough- which it wasn't doing before. 

For the rough idle it may have to relearn the idle speed as the battery was most likely disconnected and removed.

Need to take it back to the shop that did the work and have them look it over. If it smells like gas that usually means there's a fuel leak somewhere and that's a fire hazard.

Probably has the timing off a tooth or the AVLS is screwed up. The rocker assembly on those heads is quite complicated.

 

GD