2002 Volvo S40 problems?
 

Okay so recently my 2002 Volvo s40 started having this problem where it shakes & the rpm will rev up by itself in park. This causes the headlights & dashboard lights to dim and light back up. The car sounds like it's about to stall out but hasn't yet. I thought this was the battery but I was reading other forums on the fuel injector regulator. I pulled the dipstick out & it smelled like gas which was one of the signs. I just changed the spark plugs because the 1st and 4th cylinder misfired & I wasn't able to go up hills more than 15 mph. It drove like a tank for about 3 days but then sounded like it was gonna die again while idle in park. Anybody know anything about this?