I checked the spark plugs and it does in fact appear that the engine is running rich, but can the O2 sensor be the only cause? I don't want to buy one, and then the CEL is still on. Another thing, I notice that every time I reset the computer, it takes about 50 miles for the CEL to come back on. If I were to get my car inspected while the CEL was off, do you think I would pass inspection?