My 2000 CR-V runs great at start-up, 1800-2000 R.P.M.. As engine warms up and R.P.M. drops, engine starts to miss around 1500 R.P.M. and gets worse as speed decreases to idle. At times will sputter and quit when at idle. OBD scan showed multiple misfires, so changed spark plugs and plug wires. Checked timing belt and timing was perfect. New plugs and plug wires made no difference, still runs the same. Any ideas, anyone?