hey guys, I have a 1997 grand prix GT. I recently top swapped it. I got an air/fuel gauge hooked up yesterday and it says it's running lean. It drives perfect until its at idle. The RPM's drop down to like 400 and then jump back up to a normal idle. I have an alternator voltage booster so im running at like 15 volts, and when this happens the volts drop down with the RPM's to like 12 volts, and then slowly go back up to 15. This only happens when the car is warmed up.. please help!