'96 s10 4.3l x(csefi) 5 speed ext cab 160k miles.

So I had the friendly folks at o'reilys use the scanner on my truck and I got a code.

P0140 Down stream heated o2 sensor insufficient activity (bank 1 sensor 2) It says the same thing for that code in my haynes.

The only symptom I have is at idle the rpm will bog down to about 500-600 for a second and then settle back to about 750 where it normally idles. I'll do this about once a min while at a stop light. Some days I don't notice it at all. Everything else runs smooth. Sometime it smells a little rich when I shut down the truck.

3 questions:

The list of fixes from o'reilys seems to point to actually replacing the o2 sensor since theirs no other codes. I always been told though that usually the 02 sensor is a symptom of something else.

My Haynes is a bit confusing? Do I have 2 or 3 sensors on my truck and which sensor is bank 1 sensor 2? It says I need to test all 3 but only give testing procedures for 2. I would think that the downstream sensor would be the 1 behind the catalytic converter but haynes says that is bank 1 not bank 2.

Can you clean them? I've heard mixed results. Haynes says don't use any cleaning solvents but my carb/throttle body cleaner says it's o2 sensor safe.

any ideas?

 

Bank 1 is the bank with cylinder 1 and Bank 2 is the bank with cylinder 2. When they say a carb cleaner is safe for the O2 sensor, the mean it won't hurt the sensor when sprayed into the intake. It does not mean it is safe to clean the O2 sensor with it. You have 4 sensor on your truck. 2 on each side. Bank 1 pre or upstream would mean the side with cylinder 1 and the sensor before the catalytic converter.