my friend has a 94 celica gt and whenever she drove it the idle would make the motor shake like crazy. then a few days later it would just shake whenever the car was on. so yesterday i went over and looked at it, her spark plugs were REALLY LOOSE. so i tightened them down and sprayed some throttle body cleaner in and checked her fuel filter and air filter. it ran great all day yesterday and today she called me and said its doin it again. does anyone have any idea?