I just installed my tanabe exhaust on the is350..first I notice that the rpm on idle is higher than stocks..secondly i notice when i am in the 3000-4000 rpm, after pressing the brake, the rpm needle decreases..however when it reaches lower than 1000 rpm or so..the rpm needle automatically jumps back up about 300-500rpm..is this a problem? Also the left exhaust seems to be a little bit lower than the right one...