Thread: RPM drops while driving

at 65 mph on the highway my rpm are @ about 1800 or 2000 but still drops after a while it use to stay around those numbers before. but it also drops at low speed to like driving at 35 or 40 mph I've been reading on the inter net that a bad coil park can caused this to happen to is this true. And one other thing at idle it shakes a little bit not hard but lightly like its misfiring