I recently replaced my opti and did plugs and wires cause my car was bucking and misfirieng and idling really rough. After install everything seamed to be fine and ran really well for 4 days until yesterday I had them inspect it and after getting my car back it just started doing it again. Car seams to be runnning really rich, could this be part of the problem? All mods should be in sig.

 

If I had to guess I would say you burnt up one of the new plug wires on the headers.