So I'm have some problems with my 05 cobalt. The car runs and drives but when you slow down I'd say 96% of the time the RPM will jump slightly then stall out. When you start it it idles kind of rough. This will happen 2 or 3 times and will act fine until you take your foot off the gas as your braking. If you put it in neutral while you idle it smooths out. The only code I pull is a p0402 I checked for leaks and have not found any. I replaced (for other reasons) the fuel filter, spark plugs ignition coil and ignition control module.