okay i posted a little while ago about a code 21 i just changed my spark plugs, and the cel went away for about an hour, then came back on. Is this because i unhooked the battery and it took a little while for the car to figure out what was going on? The only gauge i have in my car right now is boost, i havent installed the others, but im holding back on boosting until i get these in. Ive been told code 21 is the 02 sensor, could i be getting this because im running lean?or too rich?