Just recently purchased a 2011 PPV, ran like crap when I got. So far I have replaced plugs and wires, new air filter and cleaned the throttle body. Runs a whole lot better now but when I am coming to a stop the RPMs drop below 500 and shudders a bit then levels off then the RPMs bounce around until it settles, 30 seconds or so. I am not sure what else to do besides replacing the coil packs maybe. Currently running Premium. Any advice is much appreciated.