My 289 will idle at 2000 rpms, and when I put in drive, it will drop around 1000 rpm and would unintentionally raises and lowers it rpm aroun 500 to 1000. I rebuilt the carb, replaced the fuel pump, spark plugs wires and distributor cap or rotor, and also tuned the idle, but will do the same thing at any idle speed, I am wondering how to fix the unintentional acceleration?