Check engine light

I deleted your other thead because we do not need multiple threads for the same problem and it would just confuse people. Just post updates of this problem in this thread. I posted the info you put in the other thread in your original post above.

Well anyways. that is a slow response on sensor ho2s21 or the upstream sensor on the drivers side.

If you have a exhaust leak you could get this code. Also if the sensor is not getting hot enough you might get this code. If you do not have a exhaust leak I would test voltage on the heater circuit of this sensor. If you are not getting full power to the heater circuit then the sensor might respond slowly.

Is there any other problems you are having, like bucking,hesitation,misfires or anything else.

bluesonic said:

The two other things I think I've noticed is that the engine idles a little "rough" for a few minutes after a cold start and I don't know whether its my imagination or not but the exhaust on the driver's side has a stronger, more acrid smell, you know , kind of burns your nose a little. Like I said, I don't know if I'm just imagining it since I knbow something's wrong or not. Thanks for your response. I'll try to check that other stuff out too.

Bluesonic

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it is possible to smell a difference in the exhaust even with cats if you have fuel mixture issues. If a lot of fuel is being dumped down to the cats the reaction of that can cause a difference in exhaust smell.

Check the heater circuit to the O2 sensor. Additionally, it might require replacing the sensor.

If you have changed headers relocating the sensor, this might be your problem.