What causes intermittant code P0193?

I appreciate the answer. I replaced the FRP and the light was still on. I disconnected the battery for a while, removed the computer and cleaned evey metal to metal point I saw and applied a little silocone grease. I also scraped away the paint from the firewall where the double ground wire was attached. The light then went out. From all my other readings I decided to replace the upper and lower intake gaskets and injector o-rings; it was time for new spark plugs anyway. Tribute is smooth running now. Thanks again.