The PCM will need to be tuned.

I just had this same thing happen to my 03 SSEi two days ago, checked the plugs and wires and all checked out. Dan suggested I check the coil packs and turns out my 2 week old coil packs had gone bad. If you have checked everything else give that a try, they are very easy to replace.

Lean can also be fuel pump, fuel pressure regulator, bad injector. All things that should be tested for and scanned for. Most likely a one cylinder misfire is plug, wire or coil related.

One thing to watch out for with #4 and #6 misfires is that the wires aren't touching the O2 wiring.

I notice recently the smell of gas after shutting the car off, any ideas?

Is the smell coming from under the hood? If so, check for any leakage around the fuel rail connections, also around each injector.

That'* a pretty vague statement. Without us being there, the best suggestion is the obvious one that sounds pretty sarcastic. "Find the leak"

Check the gas cap, evap connections, fuel line connections and review the injector o-rings.

I might take the valve cover gaskets off and check all the fuel injectors and possibly replace the o-rings. I know my state was very vague but again I haven't had time to actually take a look in the engine bay. My engine has 137k is it a good time to replace the injectors?