Originally Posted by PaulReynolds

My duty cycle is bouncing around 55-60 at 2500 rpm, and 45-50 at idle.

So from what your saying, even if I lean out my idle adustment a little, the only time that will change any thing is during the warm up cycle?

YES

Also this would mean, I guess, that if you run a CO sniffer in your exhaust while tweaking the mixture, and the car is fully warmed up, the feedback system would negate any changes you are making with the adjustment screw (unless you go to extremes), and the CO content would remain unchanged even though you are turning the set screw?

YES, AS LONG AS YOU DON'T MAKE SUCH A LARGE CHANGE IN THE BASIC MIXTURE ADJUSTMENT THAT THE LAMDA SYSTEM HAS INSUFFICIENT CONTROL AUTHORITY TO CORRECT IT BACK TO STOICIOMETRIC.

If so, then if a car was truly out of spec (running abnormally rich all of the time, even when fully warmed up) how in the world do you adjust the mixture? Or would this be pointing to a sensor or mechanical failure?

YOU WOULD HAVE TO LOOK FOR A PROBLEM IN THE LAMDA SYSTEM, BUT YOUR DUTY CYCLE READINGS TELL ME IT'S FUNCTIONING PROPERLY.

I just want to make sure that I understand the system. I spend a lot of time in bumber-to-bumper traffic, and was hoping that a slight tweek toward the lean side might help me. But if it is only going to make a difference during the warm up cycle, this won't help me much. I have a 35-40 minute drive to work, but the bumber-bumper doesn't start untill after the car is fully warmed up anyway.

AS LONG AS THE LAMDA SYSTEM IS OPERATING CORRECTLY, AND IT SOUNDS LIKE IT IS, THERE WILL BE NO EFFECT.

I think that you are telling me that I should leave it alone. You're probably right. The car starts cold fine, idles cold fine, transitions into closed loop flawlessly, and has great all round driveability. Exhaust does smell a little rich even when the car is fully warmed up, but I guess that this can't be changed.

CORRECT

Anything else that I should check to see if a can get a little increase in MPG? Plugs, wires, oxy sensor, air filter, fuel filter, etc. all new or young. Car runs great, closed loop system seems to be working, just doesn't seem to get very good mileage.

Thanks,

Wayne