Adjusting the timing on your 240sx
Fully warm up the engine. Shut engine off. Disconnect the TPS harness connector. It’s located on the passenger’s side of the engine just above the throttle assembly.
Attach timing light. Start engine and set timing to 20 degrees BTDC. Check the idle speed. It should read 650 RPM; If not, adjust the idle screw until you get 650 RPM. The idle screw is located on the passenger’s side of the engine near the firewall below the intake manifold. Stop the engine. Reconnect the TPS harness connector. Start engine. The idle speed should now be 700 RPM.
That’s all there’s to it.