1998 volvo s70 fault codes P0455,P0172 and P0302

1998 volvo s70 5 cyl(no turbo) 120k miles. car began to run a little rough and engine lights come on. checked codes and found 7 faults and 3 pending. P0172,P0505 and P0300-P0305. three pending are P0455,P0172 and P0302. what can i do next to find out more of these codes and get to the bottom of the problem w/out going to dealer or mechanic. any help is appreciated. rick
When was the last time this car had a good tune up
With the codes you got i would check your fuel pressure
and fuel filter as well.