My '05 Chevrolet cobalt 4 cylnd. Has been puttering badly, acts like it wants to cut off, sometimes it does at a stop. Had engine replaced with '06 engine roundabout a year or so ago. thought maybe bad gas. Put sea foam in it same results. Had test done read code: P0300..misfiring. replaced knock sensor and spark plugs. Same results. Any ideas?
You may also have a problem with the cylinder head and valves. See this link for information onChevy Cobalt P0300 at Idle