The rear O2 sensor was replaced due to damage (pic below) & the cat was deleted.

There wasn't enough room to put in the O2 extension bung as the new O2 sensor is longer than stock.

The code for the downstream O2 sensor has gone away but I'm still getting P0300 and experiencing a CEL and a very rough idle under load (misfiring).

Thoughts?
Where should I look next?

History:
The plugs were replaced about 15K miles ago.
The fuel pump was replaced last Summer after getting a code for low fuel pressure & confirming low pressure at the rail with a rental gauge. A connector on a small hose was damaged and taped up when replacing the pump. If that connector was on a fuel vapor recirculation line, could that cause P0300?

I previously sprayed starter fluid on the (PCV?) hose (always seems to be some oil in the TB) and brake booster hose and the idle didn't change.

I'm at my wit's end as this is my daily driver and it's not been drivable for a week.

 

What spark plugs did you install? Anything other than ACDelco 41-103 (iridium) plugs usually cause problems.

And as mentioned earlier, you may need a new throttle body.

 

Thanks SS 350
I replaced the plugs with ACDelco Iridium 41-105...did I screw up (it's the recommended plug for 2006, 2.2L's...did I mess up).

 

Starter fluid?

 

It supposedly will increase the RPMs if it gets pulled into a vacuum. I'm no mechanic and am way out of my element with modern engines (I miss carburetors).

 

But the starter fluid of yesterday can destroy the sensors and aluminum parts . That just might be the source of the problem.
use throttle body cleaner spray, CRC offers a good product.

 

Wrong plug number. Should be 41-103 ACDelco.

note. Odd that I looked in the 2006 Owners Manual and it shows 41-981. Guess that number has been superseded ?

 

"41-981 is the old part number, which was a platinum plug. 41-103 is the iridium replacement and superseded 41-981."

 

A friend has a smoke machine I might be able to use this weekend.

I use CRC's MAF, TB, & intake cleaner whenever I clean those parts. They make great stuff.

Good to know about the starter fluid. It was just used in a quick, short, shot at a vacuum line to see if the RPMs increased.

 

Is that a picture of the old O2 sensor? It should be gray/blue dry clean. You are burning tons of oil you Cat is getting trashed .And all the attendant problems.