hey guys my 98 4cyl accord auto has rough idel when coming to spot the car shakes and it if feels like its gona turn off i put new sparkplug in there (OEM NGK vpower) and has a new cap and rotor that i replaced last year (NAPA) the wires are still the stock ones that came with the car...i noticed in my exhust there is a lota black stuff building up....and i also own a 94 accord and a 2000 camry i check the exhust on thoes cars its not black at all...can anyone help with diagnosing this problem.