Need help with engine codes
 

My 99 es 300 ran absolutely perfect, then today it started idillling rough, the check engine light began flashing on and off, Checked codes and getting a P0303 misfire, and a P0171 system too lean bank one error. Are they related ? does anyone have any advice on where I should begin ?

Your #3 cylinder (Rear, middle) is not squirting enough fuel, causing you to run so lean, you're mis-firing, or you've got lame spark & you're mis-firing.
Pull the intake off & check that the fuel injector wiring, and the fuel injector itself.
$$$ is on the fuel injector wiring.
BTW, run to an autoparts store with $10-15 & buy some NGK 5553's. Just say, "I need six, NGK five five five three's. No, five FIVE FIVE three. You got it!".

And um... Clean the IAC valve, EGR valve & throttle plate as basic mantinance while the intake is off, Clean the inside of the upper/lower intake as far as you can reach & gain 5-10bhp from it. (Well not *gain*, but gain back some stock power & responce)

UPDATE.

Changed out the plugs and still running rough, switched the coil pack from cylnder 3 to cyl. 4 and sure enough got a P0304 code instead of a P0303 code.

Culprit >. Bad coil pack, installed new one now car runs like new again.

93 es300
Do you guys know what my HVAC codes mean? 11,12,13,14,21,22,41,& 43??