simple arduino codes

hello again i need as follows - a mosfet to act as an inline relay to control power to a iginition coil (four coils to be controlled by one mosfet just to get or to not get 12v, ground of each coil pwm controlled via ecu) - i need to map an input value that later is dependant of a potentiometer signal lets say first input i have x revolutions per minute and a given value of a potientiomenter and depending where this one is it will have to move a stepper motor (that actuas as a flow valve) to certain degrees of open or close, higher pot value more open and smaller values less open. by the way, say hay pete so i know you have read this the stepper needs first to "learn its position" from 0 to 90deg via consuption hitting the lock point (higher power drain) not via end run switches, this is to controll a exhaust valve.