my dad has a 2000 volvo s70. he just had the starter replaced at a mechanic as the car wouldnt start. now the car has suluggish acceleration and turns off when driving. when you turn the car on the rpms keep on going up to around 1500 rpm then go down until the car just turns off. i recently replaced two ignition coils on the car because of 2 misfires. i believe this is a problem with the fuel system. what do you think i should check and how to diagnose what is making it turn off.thanks