My car has been running rough lately and shakes a little bit, it even tripped the check engine light. I had my mechanic look at it and he says he's not sure, but that the spark plugs were tightened too much and he didn't want to risk stripping the head by forcing them. Any idea on how to losen them up? They were installed at 75K miles and I'm at 97K now. My mistake was letting my friend tighten them instead of torqueing them to the right setting. Also, the mechanic said i should have put anti-seize on them because it is an aluminum head. Any help would be appreciated.