From the forums I've read I should try to tackle the following along with the Coil Overs and plugs...
"intake manifold gaskets, throttle body gaskets, plenum gasket, thermostat, pcv valve.. You'll also need some spray to clean the mass air flow sensor."

I also queried a bit about the oxygen sensor and it looks like I should replace my pre-cat ones anyhow given my mileage. I know they're are two upstream ones. Is the one not mounted to the exhaust manifold easy to replace at a later time?

Note: my mileage is 16.4 MPG which I consider poor. I am hoping this may improve things. I have no clue when these were replaced last but I did replace the front three plugs last year.


Which O² Sensor is it?
Manifold Gasket
Thermostat
PCV Valve

Are there any sensors I should replace?


Note: 2007 AWD 255,000 miles. Codes are P0355, P0300, P0301 Cylinder 1 (Closest to Driver)

Suggested Tool set and consecutive upgrades

 

Did the same maintenace a couple months ago. I did not need the special plug wrench just a narrow regular one worked just fine, also didn't see any need for replacing any of the gaskets you mentioned. My PCV valve neede replacement badly, likely original with 160K miles. Front plugs took minutes, rear took maybe 3-4 hours but straight forward. You may also want to check all your vacuum lines a at least one of mine was old and cracked, they're cheap and easy replace them all. Engine air filter, spray clean your MAF, wipe down/clean throttle body. I drive pretty mild so average mpg with 2004 RX330 AWD on level ground is 22-27 seems to vary dspite my driving being pretty consistent

 

I would just replace cylinder #5 coil, and all the bank 1 plugs while you are it, clear all the codes and go from there. I see no needs to mess with intake gaskets unless you are getting lean fuel trims.

 

Have your valve cover gasket been done recently? They aren’t leaking?

 

No I have not replaced the valve cover gasket. I haven't seen any oil around it. How would I ascertain if this may be an issue? low pressure? I just feel like i get absolute **** mileage. 16.5MPG. I'm a bit incredulous at the 22-MPG for the AWD RX330 he mentioned. At 260k miles I consider gaskets to be part of maintenance. I just don't know which ones to replace. Also, the exhaust manifold is at the rear of the engine; correct?

I believe my upstream O2 sensors are due as well. AFAIK not much of anything has been replaced aside the plugs at some point.
I'd also like to replace those two little VVT screens lol

Right now I can't drive the vehicle.
Thanks for advice btw!! I just got a 0.09 DUI so I'm trying to juggle that too without the vehicle atm

 

Check your high pressure PS hose. If it looks rusty, I'd get that as well.