98 240sx unsmooth idle and a MIL, im stumped

[JXN]

Hi,

I have came to a problem that I could not resolve. Maybe you guys can help me a little bit.

The problem:The engine is not idling smooth. And fluctuate from 800 - 820 RPM. Also, took its giving a MIL for running LEAN. Checked spark plugs, the white tips on the tip of the spark plugs indeed indicate that it was burning lean.

About the car, it has 106k miles. I just changed the spark plugs. Becuz I thought it was bad spark plugs. Runs fine when its not idling. No lost of power. Just took the throttle body and intake mani off to clean. reset the timing and ECU. Problem is still there.

First thing comes to my mind, fuel pressure regulator??? But then again, i dunno....its unlikely it would just malfunction. Everything in teh car is stock.

Any tips or advise would be greatly appreciated.

[3Q Jay]

what is your fuel pressure at idle (measured on gauge between fuel rail and filter)? then do that again with return fuel line pinched. also check fuel pressure with key on, no start (should be higher than when idling, since no vacuum).

did you install OEM (NGK) plugs of the correct heat range?

also suggest ohming your injectors.

[JXN]

I didnt test the fuel system yet, I was hoping that its not the fuel system. But I will definitely look into it.

I did install the NGK plugs. Will check for heat range. Thanks.