Interesting question regarding the sticky lifter. I don't know for certain how that might affect the things, but it is worth thinking about. Don't confuse me with a real expert on combustion (like Mittenhed), but after some reading on the subject, I do believe that there is a limited margine of tolerance regarding the feedback from the O2 sensor. What I mean by this is that the fuel mixture must start out fairly close to correct or the feedback that the O2 sensor provides to the fuel managemnt system can be 'confusing' and the system may try to overcompensate.

Example: NOx is normally associated with a lean burn condition. However if one cylinder has a periodic misfire, this causes the O2 sensor to report a rich condition and the Fuel management computer compensates by leaning the mixture. The resuslt is a mixture which is far too lean for the other three cylinders that want to work properly. This lean condition on the three cylinders results in high NOx content. Sure HC will be out of spec also, but the point is that the feedback system is not working as designed because the feedback variable is out of range and the computer is overcompensating from the faulty input.

I can imagine a sticky valve causing a similar experience. Like I said, I am not an expert, but I would like to know what someone with more knowledge and experience has to say about your question.

Do you live in an area where they require emission testing. In St. Louis we are requied to test every two years and any time the car changes owners. The result is that you can have your car tested for $20.00. In theory, owners are obliged to provide a clean emission test when selling a used car, so a random request to test is not unusual. Our testing is fairly rigorous, however, we don't suffer any long term negative results if the car does not pass. You are entitled to work on it yourself and get it re-tested for free. If this is so in your area, it might be worth a small investment to find out what is coming out the tailpipe.

Good luck,

Dan