First of all, stock engine, ECU, exhaust, etc. No under hood mods. It idles rough at around 750 but is smoother at 1000; but when held at constant throttle above that it will surge up and down about 250-500-rpms. It also failed smog inspection last time but I have since adjusted the TPS and it seems to be running better at idle (it only failed the idle portion of smog, not the 2500 rpm portion.) with no more bucking at low speeds. It didn't start surging, though, until the dealer adjusted the idle for me. I've tried adjusting the idle myself and it doesn't seem to make any difference.

I've changed spark plugs and they all look the same, with a fine black coating that make me think it's running too rich. New plugs made no difference.

According to the manual the possibilities are: injectors, fuel pump, pressure regulator, spark plugs, O2 sensor, or knock sensor. Mine is not an intermittent problem, it's very constant, so could one of these be the culprit? I'm not thinking it could be fuel problem because of the black plugs and the too rich smog failure. O2 sensor? Knock sensor?
Thank you in advance for any help you can give me.

 

I would say temp sensor, tps, or map sensor. 02 sensor will not cause the car to idle bad just use more fuel.

Jeff

 

I will admit my ignorance, where/what are temp sensor and map sensor?