I'm in the process of changing my valve cover gaskets and seals on my 05 RL and noticed that bank 2 is dirty as hell and bank 1 is perfect looking. The car drives great and I've changed every fluid there is to change. It has new plugs and I don't use cheap fluids or parts. The only issue I have is my millage hasn't gone above 11.8 mpg and I do have a P0430 code. The driving is probably 99% around town.

 

I'd say check the breather pipes are clear, etc as a first step.

I note the EGR valve is on that bank, but I'm struggling to see how it would cause that. It could explain the P0430 code though.

If the rear spark plugs are loose, perhaps the rear bank is running cold and inefficiently?

Just guessing, really.

 

Thanks for your thoughts, I'll check everything. What do you think about my milage? Is it typical for an older RL? I don't drive like a madman or anything. I was thinking about changing the o2 sensors, any thoughts on that?
I do plan on doing the cat but that's one area that I'm really leaning towards aftermarket. Any suggestions on a good one for my car would be a great help.

 

I get around 16 (Imperial) MPG driving around town (bit of a leadfoot) so I'd say yours is definitely running rich.

O2 sensors are probably another 'easy' check - if you can unscrew them.

That sort of gunking seems to be a common problem with VCM-equipped J35s - I found this thread which might help:

Here

 

That's bad MPG even for the rather thirsty RL. Even in town, you shouldn't go below about 14 unless you're an absolute leadfoot.

 

I actually drive more like an old lady. Once in a while I step on it to see what it can do but I'm mostly real easy with it. I just put a new bank 2 sensor 2 in and my milage actually went down by almost a half mile. I'm probably just gonna have to bite the bullet and change my front cat. Any suggestions on good aftermarket? I did check the temp coming in and going out and it was almost equal, just a 20-30° difference

 

i believe the discoloration is from heat..