Nissan ka20 rough idling but all plugs are working ,on inlet pipe of fuel there's pressure but on return there's no fuel comes

black smoke indicates oil getting into the cylinders , get the compressions tested as a first step

You should check your exhaust for a clog of some kind such as a collapsed catalytic converter,Muffler or bent pipe or even something put in the tail pipe. also air filter car will start and run with clogged air or exhaust at idle but will starve out when idled up at all

rough idle is a sign of air /fuel mixture wrong
check for vacuum leaks in all vacuum hoses including those under the dash and the transmission shift actuator
check for loos inlet manifold
it can also be from insufficient fuel pressure all of which will not produce a code

Check fuel pressure. Air filter could be really clogged, usually they will collapse first. Then check for exhaust pressure out of the tail pipe. Little pressure or it's really hot. The catalytic converter/s are plugged up.

If your still having the gas smell problem or found a solution to the rough idle problem, contact me at [email protected].

i solved the gas leak, still searching for cause of rough idle.

I had the same issues, after replacing the ECU temp sender under intake manifold, the Airflow meter-even though it tested fine, having the injectors cleaned by one mechanic , having the codes read by another mechanic and testing ok and discovering they had no O2 sensor to replace. I pulled the feul pressure regulator off and found some f-wit had blocked the rail side opening with a bolt Put a new one in $120 and she runs sweet.

blown head gasket. black smoke means that oil is getting into the cylinder.

1st I hope you are taking the fuel pressure from the correct side of the system. The correct side will be the side coming from the fuel filter and before the fuel pressure regulator. At a normal idle, the pressure should be roughly 30-33 psi. When you crack the throttle rapidly, a sudden vacuum drop will cause the diaphragm in the fuel pressure regulator to shift causing the fuel pressure to jump sharply. Usually to 45 or 50 psi. You can check the maximum fuel pressure by dead heading the pump. This can be done by simply pinching off the return hose to the fuel tank. At an idle, the maximum fuel pressure the pump will put out will be displayed. You will also notice a slight jump in rpm's because it cause the fuel mixture to fatten up before the ECM can respond to changing the pulse width based off of the o2 sensor.
I hope my answer was satisfactory.

i have a nissan b-14 idle roughly sometimes cut off when in traffic. any solutions???????