Hi and welcome to NICO Club!
Sorry about the smog issues. It's good you had a smog test because these poor numbers mean it's not running that well. There's some stuff to do. One is to get OBD-1 codes from your ecu using the lights. You did something like that, what code numbers did you read off? There should be at least one code, 55 if all is well. Don't forget to put the ECU back into Mode 1 when your finish pulling numbers.
Here's what I suggest. Install a new fuel filter and run some injector cleaner through the system. You need your fuel delivery cleaned up a bit I think. Use premium 91 octane for this and until you pass your smog test. Spray a can of carb cleaner around your intake top, bottom, front, back and side and up the line to the brake booster while the engine is running and make sure you don't have any vacuum leaks (do this before setting your timing). Also, check the resistance of each injector with a voltmeter and see what Ohms you get. Check voltage on your TPS. Get a timing light, a screw driver and a socket. Use the FSM procedure and set your idle (with IACV screw) and timing (rotate your distributor).
If you have no codes, then your sensors should be fine. If codes, then replace. O2, TPS and MAF are the main ones for this stuff. Please keep us posted and ask any detailed questions as they come up. Good luck!
Go here, load PDF, hover over the upper right hand corner and an arrow icon appears, use that to download the PDF to your device...
http://www.nicoclub.com/service-manual? ... 1993_240sx
PS - you have a CAT on there right? It's not hollowed out? Gonna need a working one of those... the exhaust smells funny when these go bad, like rotten eggs.