Hi, here are some things you can check first, condition of the car's battery, check the
ground connections of the battery clean the connections , also only put premium gas
in the car,but for all the problems you described I heavily suspect the ecu of the car, for
programming ,this can not be done with autel products because Porsche only allowed
dealer scanners to do these jobs. The given price of 750 usd sounds reasonable to me.