Smoke from exhaust while idling and Check Engine Light

Hey guys, I've got a few questions. My Check Engine light came on a day after I installed the header, but the car runs fine. I got it to turn off by unplugging the battery but it came back on 2 days later, could my O2 sensor be going bad? Like I said the car runs fine, so I've lived with the light being on but now it's getting annoying and I just wanna know what the problem is.

Also, a blueish smoke started coming out of my exhaust yesterday. The thing is it only smokes while it sits at idle, but doesn't smoke while I'm driving. I don't think the problem is sever since the smoke doesn't occur while I drive. I'm pretty sure the Valve Stem Seals probably need replacing, since if the seals are bad oil builds up in the valves. I've checked the oil level and it checked out good, in fact it was right on the mark. I also change my oil every 3,000 miles, it was last changed in the beginning of April, I check the level every Saturday and it's been good ever since I changed it.

What do you guys think?

how many miles do you have on the car? if you have more than 100,000 miles on the car I would go ahead and replace the o2 sencer. They useally go out at about 95,000. The smoke thing I really don't know about.

Wow... A dollar short and a day too late...

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