I have a 2000 Nissan Xterra with 2 error codes: PO325 and PO303. What needs to be repaired/replaced?

You can tryhttps://big-manuals.com/products/2001-nissan-xterra-service-repair-manual ... stuff likewiring, schematic, electrical diagrams, torq settings, parts info, error/fault codes, full assembly/dissembly, service instructions and a lot moreetc are basic contents of these online books they here on this website

TPS sensor (RPM) po120,knock sensor po325.

underneath intake manifold between cylinder 1 and 2.

code p0325 refers to knock sensor (KS) 1 bank 1 circuit malfunction===causes wiring--poor connection--KS needs replacing.

THROTTLE POSITION SENSOR, MISFIRE, #4 MISFIRE, KNOCK SENSOR, THESE ARE YOUR TROUBLE CODES, PO120,PO300, PO304, PO325, RESPECTIVELY, REPLACE THE TPS @ THROTTLE BODY, REPLACE KNOCK SENSOR , @ ENGINE BLOCK, REPLACE YOUR SPARK PLUGS & PLUG WIRES ! AND YOU MUST ALSO REPLACE BOTH YOUR AIR & FUEL FILTERS, DISTRIBUTOR CAP & ROTOR , INSPECT, MAY NEED TO REPLACE, I WOULD ANYWAY !!!!!!!! ADD SOME GOOD FUEL INJECTOR CLEANER TO TANK, NEXT FUEL UP !

maybe a haynes repair manual would help.check your auto parts store or on ebay

I had a 2001 nissan xterra in my shop,and it had the same codes. there is a very common problem with the distributor on nissan 3.3 motor. I am not sure where you are,but get a price for the distributor. I got one from ebay cheap

Check for engine vacuum leaks, use a can of spray carb cleaner, if you hit on a vacuum leak the engine idle will change. Repair *** necessary.

You got a timing chain
Injector cleaner,in my opinion is a waste of money
PO306 could be a missing coil on cyl #6,still should start
PO325 Knock Sensor-most likely okey
Plugs,cap and rotor,will not prevent it from starting,it used to run with old parts, before the current problem!

I suggest you make sure you got the plug wires on correctly and number them with a ball point pen,on both ends.
Make a diagram of the dist cap wire locations.
Check out the TPS Sensor and make sure you have all intake ducting in place. You need the MAF Sensor in the system to run have it run
Have you checked fuel pressure? The pump may be going bad

po325--ignition system or missfire.