I'm trying to help a friend of mine, she has a 1998 Camry and recently had the sparkplugs changed because she was getting a CEL for misfiring. She's still getting a CEL but this time its PO300, PO302, PO304, PO306 and PO171. I suspect a vacuum leak somewhere but I haven't been able to hear any noticable ones. I also don't know if the correct plugs were used but I would think that it would misfire on the other bank as well if the plugs were the problem... any suggestions or feedback would be appreciated. The car has 77k miles. Thanks in advance.