katheo

hi, I'm not too knowledgeable about car repair. I was trying to do the right thing for my car (1995 Legacy LS wagon) & I bought a new air filter & spark plugs at the local auto store. I went in to the store with the proper spark plug numbers from the owner's manual. The guy at the counter said they didn't have that one but he cross-listed it and said the Bosch were just as good (I didn't know any different). I took my car into the repair shop for a oil leak problem & I figured that since it was going to be a while until my father could help me replace the spark plugs, I might as well have them replaced while the car was in the shop. When I went to pick up the car, the cashier guy told me that they replaced them, but I shouldn't buy Bosch in the future. He said the guy at the auto store was wrong and the Bosch weren't just as good for Subaru's. It seems to me that the idle knocks more than it used to (but it could be that I am just listening more closely). My question is, how bad is it to use the wrong brand of spark plugs? I don't want to do any damage. Besides that, I wanted to get the best gas mileage I can since gas is expensive these days. Will using the wrong brand affect my gas mileage or performance? I think I would like to buy the right ones & have the shop put them in so I don't have to think about this again. Should the repair shop do this without charge since they should have known better than putting in the Bosch? (they want to charge me for another hour's worth of labor). thanks for any comments & suggestions!