Stock engine, K and N replacement filter (not cold air) and cat back Flowmaster. Cannot get it to keep from knocking. Been to a number of mechanics, tried different gas (run 91 now), checked all the normal stuff (plugs, etc). Consistent advice is to get it chipped/mapped/dyno'ed, but lowest estimate is $800+. Suggestions? If I have to chip it, what brand/kind? Any other options besides having to chip it? I really need to keep the cost down, but it sure is irritating to not be able to drive this car with a little enthusiasm. I live in Los Angeles area, if that helps.