Hi. I have a 98 rav4 that has been losing power when accelerating from a stop, a little rough cold start (I need to give a little gas sometimes) and really shaky and stutters going up inclines. If I give too much gas....I get a flashing CEL but it'll go away after I ease off gas. I took it to a mechanic and unfortunately I had the day before replaced the battery, therefore losing all codes in the computer. But the determined that it is PROBABLY the Bank1/Sensor1 (A/F sensor?). I'm in CA so based on my research, I'll need a CA emissions certified sensor? They want to charge $400 for this repair......I want to do this myself. Apparently theres only 2 of these sensors on the 98 rav4? Do I have to go with Denso? Any advice?