I swapped out the stock plugs (78K) with the one step cooler NGK Iridium IX BKR7EIX-11 plugs (15% pulley). What a difference. Anyway, after a while the service engine light came on, so I checked the code and it said "lean condition bank 1". I drove it for a little while, thinking maybe the plugs really needed to be changed and the ECU needed to adjust. The light went out after probably 100 miles. So I am thinking all is good. But then it comes back on a little while later. So I pulled the plugs, and it is definitely running lean, especially in cylinders 1 & 2. Put the old plugs back in, drove to and from work (50 miles), the light goes out as soon as I start it at work. Pulled the plugs this morning and all looks normal. Any ideas? All in all I probably had a tanks worth of gas before I went back to the old plugs.