Nissan Repair: rpms up and down, vacuum leak, ok check

Question
96 nissan puck up 4 by 4 , 2.4 liter , production date 5/96 --- this start went i was driving home , like it lost 1 cylinder ,and had no power , pulled over and worked the gas , if you keep the gas in one place the rpms would go up and down and black smoke out the tail pipe , go it home
and started checking , replaceed the fuel injector , check the fuel pressure , ok , check the throttle postion sensor ,ok , checked the temp, sensor , ok , ---re started the motor and it still acts like it is loading up , but not a back but the rpm are still up and down , what would be my next move .

Thanks
William

Answer
Hi William -

First thing I would check is for a vacuum leak. Looks like you lost connection with the idle solenoid, or some emmisions vacuum circuit. Does this happen whether or not the car is cold or warm? That may be a clue on where to look.

Please get back to me on my question so we can continue diagnosis.

Thank you Will
aloha
calvin