If you know which engine you have, you should be able to find it, test it to make sure that's the problem, and how to remove and replace it, with the help of this page of the AutoZone Repair Manual;
http://www.autozone.com/az/cds/en_us/0900823d/80/16/0e/d0/0900823d80160ed0/repairInfoPages.htm
Often, they can also just be plugged up, and a cleaning out of the deposits will fix them.