Just started to notice at 4,000 to 6,000 rpm there are places the motor makes a hicup. At 4000 5000 and 6,000 almost at those marks on tach. I have new plugs but that is it.. 76,000 miles 1996 C 36. The things that have NOT been replaced are o2,MAS, coils, coil ends, wires. Got any clue what to look for? I have a Powerchip in ECU. KN filter. Of a side note.. to start the car is weird. Sometimes it fires right up.. then sometimes I have to turn it for 7 seconds plus.. when it fires it spits a small amount of black smoke that goes away after 1 or 2 seconds. When I have this long start problem the car has a cough to it and then slowly will idle.