I have a 1988 ford ranger with a 2.9l v6. a few days ago, driving to work, i stopped to buy a pack of smokes, and on my way out of the lot, the engine died quietly. started it back up with no problems and proceeded on my way. ever since then i have had a continuing problem with her running very rough at idle and having close to no power when accelerating. here is the question, as i stated it is running rough at a normal take off and idle, gurring acceleration and cruising it is also very rough, however when you get on it, she comes to life and runs fine, until you ease up and try to cruise. she acts as if she has no fire, but this is misleading as it does have great power at 3200+ rpm. i thought it may have been a fouled plug(s) so i replaced them, and while i was at it, the wires, cap, rotor, and ran an octane booster. this did nothing to help. i have noticed durring the "limp" acceleration and cruising, it billows black smoke like a chemical fire, until you gun it and the smoke stops. i know this is a fire issue, but i dont know where to go from here, if it were a bad ignition coil, wouldnt the problem exsist durring the entire rpm range? i am at a loss and do not want to go the route of buy everything and hope for the best. any advise would be greatly appreciated.