I bought my maxima 02 6spd 2 months ago,with 118400 miles on it....it had 3 owners before me , the first was leasing it...However the car whole life was in Ohio....It doesn't look that it was very very well taken care of,just the basic care ..However , when I test drove it and during my first few days of ownership , it WAS A BEAST to drive , very fun and very fast and responsive (much much fast than my previous 97 maxima automatic I traded it with)...However (by the way sorry for the long story but you might find a clue about the issue)....I changed the lower oil pan and gear oil with amsoil manual tranny fluid , back up light sensor to fix the backup light issue..however again the stupid mechanic messed a wire connection and caused high idle (1000rpm when normal temp) fixed by Nissan dealer after more than a trial to change the throttle body and removing and putting back the airbox and trying to reprogram or relearn the idle thinking its the ECU(they might mess with the timing?)...finally they discovered the broken connection to the neutral position switch on the tranny and the car idled back normal again at 650rpm... however few days after , the car started to be sluggish and P0420 and P0011 poped up on my dash and the car feels sometimes as crap...I didn't check the light immediatly (I thought It was that evap leak code as it's very common to occur in our other 2003 maxima) so I knew the P0420 around 3 weeks later....now it keeps (p0420) coming back evey 100-150 miles .... I use only shell 93 octane by the way
Now my question , What is the chance that I need a new precat (I already recieved the bank 1 precat from Magnaflow) ? is it possibly the O2 sensor downstream the precat Bank 1? but I know that this sensor doesn't affect the performance , it is just to monitor the cat,and the car definatly slower than before ? is it the MAF , plugs ,clutch ? I always use shell 93 octane...
Just another thing , the idle isn't now very smooth .. I feel the car when warm and in idle like missing or have micro-flucuating in idle speed .... and sometimes it feels like it will stall , but it never does or goes below 500rpm idle speed...Car is definitly better when cold...
your opinion please
thanks

 

Sounds like you need a precat, 99 times out of 100 it appears the 0420/0430 codes are only resolved with a new precat.

The P0011 could be a lot of things, low oil level, clogged IVT solenoid passages etc.