1996 Infiniti Q45 - Engine issues

Looses revs when stopped at lights and also jerks after I do about60 kms.Both problems are intermittent.Also blowing black sooty smoke sometimes.

Yet, no check engine light?
Your CEL might be burned out. You can still have the codes read.

It sounds like a fuel system problem, i.e., the engine is running with too little fuel sometimes (rpms drop) and too much at others (black smoke). A good mechanic can figure it out and fix it.