vn problems

Hey guys im hoping someone will be able to help me, ive had the car at a mechanic and they cant find anything wrong. Runs ok when its there

Sometimes it stalls while idling, sometimes it wont start, sometimes starts but sounds like its missing while blowing heaps black smoke out the exhaust. It can start one minute, not the next then starts fine. Can have no trouble for a day but heaps the next.
In the last year ive replaced the fuel pump and whole coil pack thing (second hand), cleaned the throttle body, which didn’t make any difference. (had same problems but now its worse)
Last week I replaced the CAS with no improvement. Ecu shows code 12
Any ideas

 

I know someone with a vp will that do? Mines a 89 model.

 

Thanks for that

 

I ended up getting a new computer and now shows code 15. Do i just replace the temp sensor? Still only shows 12 with the old.
It still has a slight miss when revving in park with light throttle.

Thanks