johnsonjay Silverado runs rough

johnsonjayjohnsonjay Member Posts: 2
edited May 2015 in Chevrolet
my Silverado runs rough when the rpm are from idle to 1500 rpms above this it seems to run much better. also when it is idling it gets the ground by the exhaust pipe black with soot. I have changed plugs, rotor and cap, to no avail. what it causing this problem???
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