Rough Idle

Hello All,

Just got my '99 Outback (2.5) from the mechanic where we had the head gaskets replaced. Made it to 160,000 miles, only real repair it's ever needed. Great car, love it. Guess it was warped pretty bad, had to have the thing decked while it was out, also the piston tops machined. Changed water pump, timing belt, t-stat all the standard stuff. Runs great now, only thing is the idle is rough, not terrible, but noticeable. Idled smoothly before the repair. Mechanic says he may have the timing belt a tooth off. I though this was an interfence engine? Will one tooth make a difference in idle or is it just going to bend a valve? Can it be something else? Some sort of intake leak? Balance issue from the piston top shave? It runs smoothly at higher RPM's just not like it used to at idle. Great independant mechanic, been with him for years, just trying to figure it out for myself.