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Got an 04 Acura TSX that's been baffling me for the couple of weeks. Accidentally bought an Upstream Oxygen sensor instead of the downstream so I thought might as well replace it since I have it (keep in mind the Upstream (Air/Fuel) Oxygen sensor worked fine before and the Check Engine light was for the downstream.

WORST IDEA EVER! Car ran very poorly! Ran lean and spark plugs turned black. Car would shudder as if it's going to stall. RPMs would go from 800 - 1100 and fluctuate constantly and this lasts 5 seconds then everything is fine. It happens when I change gear and when stopped at a redlight. I've replaced the Spark Plugs, cleaned the Mass air flow sensor, and put a new OEM Denso sensor. Still having this issue but this time it's not running lean but did pop-up these codes:

P2A00

P0135

Both codes are referencing Bank 1 Sensor1 which is the sensor I just replaced.

Any thoughts?

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  • I would buy the sensor from Acura. I have seen other sensors throw codes before until you put a factory sensor in. Although denso made the original for Acura, does not mean a denso sensor bought elsewhere is the same. – Moab Jun 3 '20 at 13:42
  • Bought it through RockAuto. They're pretty reliable with OEM parts. I'll compare part numbers with dealership one to see. – Noah Jun 3 '20 at 13:52
  • Welcome to Motor Vehicle Maintenance & Repair! If the spark plugs turned black, the engine wasn't running lean. If the engine were actually running lean, the plugs would be white or ashen white, not black. If the output of the O2 was saying it was lean, it would introduce more fuel into the mix, which would turn the plugs black. Is this a 4-cyl or V6 engine? – Pᴀᴜʟsᴛᴇʀ2 Jun 3 '20 at 14:10
  • So then it was running rich? The Spark Plugs were the standard NGK that came with the car and they were new (put in a month ago) tips turned black. It's the 4-cyl – Noah Jun 3 '20 at 14:27
  • Spoke with Acura Dealer The Denso sensor is exactly the same as the one I bought Part #: 36531-RBB-003. Should I just go to salvage yard and pull one..? At this point I'm ready to throw the whole car away lol – Noah Jun 3 '20 at 14:48

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