: I have a 89 Caravan with a 2

Hi: I have a 89 caravan with a 2.4. It was running great, my wife took it and when she got home it was missing bad at idle especially in gear, have played with rpm no difference, had to replace the head, same. I have changed plugs, wires and cap.I replaced the inj a couple of sending units. I then took it to a couple of good garages they said they had no idea. It blowes black soot out the exaust pipe. Gets lousy milage. When she gets moving she smoothes right out at road speed other than the milage you wouldn't know anything was wrong. This has been going on for about 3 years. I don't drive it much but when I do I would like it to run better. It acts like it is flooding out at an Idle.I am lost another than that the car is in excelent shape. Please help, I haave even paid an online expert mechanic online and all he said was it sounds like I have tried everything. I don't mind paying if I get help that works. Thank you