I have a97niss pick up ,when you are at at alight

What color is the smoke? Any part itself to the exhaust?

Year/make/model/engine size??????? The engine is obviously being over fueled, but without any vehicle info, supplying helpful advice is not going to happen

Yes

Can be a bad O2 sensor. Check with a scanner which shows live data the 1-1 and 2-1 (upstream) sensors. Good sensors show a rapidly fluctuating voltage from 0.2 to 0.8 V. When the sensor has a steady voltage, then its most probably bad. There is no check engine light and no fault codes set?

there is a very common issue with bad distributors in nissan pathfinders,xterras.and quest. just replace the distributor

Black smoke from the exhaust is an indication of the engine running too rich. Probably bad fuel injection system.

Sounds like the valve guides are worn. They will wear excessively due to the fact that
the gas currently sold has less lead content than what was sold when these motors
were manufactured. This also affects the rings as well. You could have the heads
rebuilt with new valve guides that are designed for the new fuel. The lead acted as a
lubricant. Also given the age of that engine, I would rebuild the carbeurator as well
if it exhibits black smoke, and replace the choke during rebuild. A sticking choke
will make it hard to start and plenty of black smoke. Hope this helps.

thats a HUGE engine and will **** a ton of gas!!! but if ts using more than normal,along with theblack smoke,tells me you have some valves with alot of carbon buid up on them.you can spend 100s removing the heads and sericing the engine....but i would warm up the engine...have a friend give it some gas to keep the RPMs up while you SLOWELY pour a ite stream of water into th carb. it will spit and sputter while you do this,dont be scared...tats normal,then have your friend rev the engine while you do a bit more. while you do this,you will see a ton of black smoke out the exhaust. what your doing is heating up the valves,and when water hits thm, it busts that build up off,and it burns giving you some black smoke. continue to do this till the smoke changes color,and then you will have fixed it. its a trick i used years ago...and never failed!!!

I had a 1995 nissan pick up with a similar problem, may want to try cleaning out or replacing the EGR valve.

MASS AIRFLOW SENSOR THERE ABOUT £6O WHEN THEY PLAY UP THE CAR WONT IDLE PROPERLY AND POOR RUNNING/HESITATES BEFORE IT PICKS UP AGAIN, NOT SURE ON THE BLACK SMOKE THOUGH, GOOD LUCK .