I think my car is working in non-loop control, since even slight changes in the air-fuel misture (my guy had richened the mixture 1/8 of a turn some time back to reduce the rough idle when cold) seem to affect the car - if the O2 sensor was working properly, shouldn't the mixture screw adjustment be redundant?
I'm getting the O2 sensor changed anyway. However, I don't think that will solve my rough running on cold engine, which is the root cause of the high emissions (since the mixture had to be made rich because of that). I've already spent over a grand on the car on this problem, with no solution, so am very wary of another tech throwing parts at me.
A very noticeable symptom in my car is that when its cold, it hesitates, and has a "slingshot" behavior, i.e., it moves in spurts. During this time, I often hear a click sound from the bottom driver side, which I can even feel in the accelerator pedal - as if something is jammed, and suddenly opens up. This happens 5-6 times, and then when temp reaches 80, it suddenly smoothens out and everything is fine.
Anyone had similar experiences? I am pretty sure its a fuel delivery problem - could it be the air flow sensor? How can one diagnose it?