Hey man if you put premium and it did run better that tells me that you have carbon deposits in the cylander. take the mass air flow if equipted off and the air filter where you have a strait shot into the intake and get a spray bottle of water and take the throtale up and down while spraying water into your intake witch if you have ever seen a car with a bad head gasket where it leaked water into the cylander it is clean as can be. Trust me with this just be carefull