I have a 97 200sx SE-R with full exhaust (headers, downtube, cat and cat back), cool air intake, NGK racing spark plug wires and NGK V-power spark plugs, and more upgrades (nothing that applies to this post..lol)...

It idles rough and noisy (off and on), the check engine light is on (just replaced the crankshaft position sensor too) and recently just started losing gas mileage and making a knocking noise on acceleration (not very loud).

Any ideas as to what could be going on? Ill take anything right now..
Thanks!

Has it been lacking in performance? Possibly a knock sensor....

Nope. Great performance. Just rough idling and all. I don't understand it lol