hey,

my friend has a 1991 subaru legacy wagon,and when she drives it fast sometimes or reg sometimes,the check engine light comes on when she drives on route 80,and when she is idling in park,the car will rev at so low sometime and then go back to reg back and forth.like a going up and down like a pulsing or what ever,

and one have this problem or know how i can fix it

Can you type that again in a way which is understandable.