Q&A

I own a 2007 Saturn ION 3. Within the last few months I have noticed the my check engine light would come on. Sometimes it would stay on and then go out, and other times it would come on and stay lit steadily for several days. The light happened to be on when my Onstar diagnostic service indicated a problem with the 3rd cylinder misfiring. The following month, the light happened to be out when Onstar performed an engine diagnosis with no problems. The light came on again and stayed lit constantly for several days, so a finally took my car to a shop for remedy the problem. The shop owner confirmed that the 3rd cylinder is misfiring, but nobody at the shop could figure out what was causing it. Ever since my car was returned to me, the light would sometimes go out, come on, and than go out again. At present the check engine light is on steadily, and hasn't gone out. Could anyone out there in the repair community tell me what could cause the 3rd cylinder in my 2007 Saturn ION 3 to misfire and what I need to do to fix it?