Hey guys i'm a newbie so I have a stock 98 grand Prix gtp with 115,000 miles on it and I've notice every now and then that my rpm drops from 2000 rpm to 1500 or 1000 rpm while driving anywhere from 30 mph to 70 mph and when I take my foot off the gas pedal and put it back on it goes back to normal for a little bit so I change my spark plugs and wires and now it does it all the time now and I have no check engine light on. anyone know what it may be