HAVE AN 01 GMC WITH A ROUGH IDLE. SHOWS MULTIPLE CYLINDER MISFIRES BUT DO NOT SEEM TO BE CONSISTANT ON A SPECIFIC CYLINDER. AS SOON AS YOU ARE OFF IDLE EVERYTHING IS SMOOTH. UNABLE TO FIND A VACUUM LEAK WHICH I THOUGHT WAS THE CAUSE. ANYBODY THAT HAS SEEN THIS PROBLEM AND WOULD HAVE A SUGGESTION WOULD BE A GREAT HELP.