I have a 99 Cherokee with 4.0 it is idling ruff. It is getting black smoke out of tail pipe. It just started the other day. I'm assuming it is getting too much fuel? It chugs a little at highway speeds if you step on it a cloud of black smoke comes out of tail pipe. I have put new plugs, wires, cap, rotor in it has helped but has not cured problem. I'm thinking TPS or Map sensor? I'm not getting any check engine light.