What would cause your vehicle to start and run but seem muffled or sound like its puttering?

plugs

You may want to check your spark plugs because mine was doing the same thing and my #1 cylinder plug was fouled out...possibly caused by bad gaskets/seals, a faulty fuel injector, or needs cleaning (pour some fuel-injector cleaner into your gas tank or complete fuel system cleaner would be better). It could be bad plug wires, faulty fuel pump, trash or water in your gas line or gas (pouring gas treatment into gas tank may help), pcv valve, clogged fuel filter or dirty air filter. My car is still broke down, even after I changed the fuel filter, spark plugs, pcv valve, my air filter looked good. Also, if the "check engine soon" or "check engine" light comes on I would suggest that you go to your nearest Autozone (free testing), or other repair shop and get it checked out (immediately if "check engine soon" light is red, which means serious problem). Yellow means not so serious on the "check engine soon" light, but still needs your attention. "Check engine" light on my wife's car is yellow, so have it checked out because I don't know if that particular light can go red. Some cars have a "check engine soon" light and some have a :check engine" light. Don't know if a car has both. If your car has a carburetor then some carb/gas treatment in the gas tank wouldn't hurt, or some carb cleaner sprayed into the carb (note that these are not the same cleaners, 1 made to go into gas in gas-tank, 1 made only for carb itself).