thardie

2004 RX-8. Had all the software updates to the PCM. Recently, starting running slightly rough, missing very occasionally, and doesn't sound "right" under load. Also, can smell unburnt fuel coming out the exhaust and there is a slight loss of power.

My OBD shows no pending codes (and of course, I have no CEL).

I've replaced the spark plugs (old plugs had quite a bit of carbon, and some orange-ish color too). No change. The only other odd thing is my OBD shows no data received for O2S11 (The Hot O2 sensor before the cat) and shows the O2S12 (the Hot o2 sensor after the cat) as wondering wilding up and down, which is supposed to be pretty constant if the cat is working. I think the cat can't cope with the unburnt fuel coming though.

It seems from this that my HO2S11 is bad, although I would expect a 0 reading from it in this case, not "NO DATA". I checked the sensor with a meter, and the heater coil in it is within spec, but the tech manual says that this sensor is current driven and not voltage driven, so I didn't try and measure its output with a meter.

This sensor is around $137 to get with the right harness. I'm $150 in to this already (from the plugs). Does it make sense to replace the sensor?

Thanks!

Terry