i have a 2006 chevy cobalt ls, for months now my check engine light has been on, code PO411. normally the car runs fine, sometimes it idles rough. the past week the idle would drop real low and seem like it wanted to stall. today i was driving and "reduced engine power" came across the dash and the car wouldn't go over 10 mph. going down a hill it would pick up speed and shift, i was lucky to get up to 25 mph. turning the car on and off doesn't help. no smell coming from exhaust, but the exhaust sounds a little like a helicopter. any ideas? thank you!