Hey, have a 1988 xj 4.0 and its idling rough and shoot toons of blacksmoke, what can cause that?

o2 sensor and map seems to be fine and working.

 

I had similar on a Subaru once. Turned out to be an exhaust leak between the engine and O2 sensor. It would naturally puff exhaust out when an exhaust valve opened, but it would also suck in air after the pulse flowed past. Then the O2 would read all the oxygen in that air and the computer would decide 'holy crap that's a lot of oxygen, dump MORE GAS!'

I'm scheduled to take delivery today of the https://nickintimedesign.com/product...ack-adapter=No to try to understand what is going on with my 88 4.0.

 

check the line from the throttle body to the MAP.