What year is your car again? S13...S14? Knowing what year would REALLY help.
Check the following items:
1). EGR valve -
a). Inspect the vacuum lines running to it - are they okay or are they torn/cracked/leaking?
b). Is the EGR valve sticking open? Take your hand & cup it around your EGR valve. Your fingers should feel the underneath portion of the valve. As the car is running & your hand is cupped around the EGR valve, pull your fingers up & gently push in the BOTTOM portion of the EGR valve. You should hear your idle start to drop - push it too fast & your engine will stall. It's possible that you have carbon buildup in the EGR valve / system. Spraying a can of carburator cleaner into the vacuum line at the top of the EGR valve & pushing up on the valve at the same time can help clean out the carbon buildup.
2). AIV valve - it may be dirty or clogged. There's a reed in there that may have gone bad.
3). Check your idle - disconnect the Idle Adjust harness..should be next to the TPS sensor - three wires...black/white/ green..???. Your car should be idling at 700-750 rmp. Readjust if necessary. Use the phillips head screw located on the passenger side of the engine towards the back of your intake manifold..almost directly below your EGR valve. You GOTTA look for it...it's hard to spot. Turn that screw accordingly.
4). Check your ground wire running from your engine block directly above your 02 sensor to the firewall to the left of the brake booster. A loose or shorted ground wire will cause a funny idle or a NO START problem. DONT ask me how I know this.
Anyhow hope this helps...
Diego
'95 SE
PS:
Have you tried pulling the Diagnostic Trouble Codes off your ECU?? To figure out how to do that go to
www.240sx.org. Click on the FAQ link & scroll down till you get to ECU..Reading Trouble Codes..SOHC or DOHC.