This could be an airleak after the airflow meter, any let breathe dragged in here isn t seen by the ECU and fittingly not compensated for and can lean the engine out and can afterward permit the engine to rev occurring considering not desired causing rasping running. As its a mechanical aberration it tends not to tilt upon the aberration open and you can sometimes listen a hissing noise subsequently the engine running.
Its as well as worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a sick pump will every upshot in insufficient fuel creature delivered to the engine. Might afterward be worth cleaning out the idle swiftness direct motor / valve as these acquire clogged up taking into consideration carbon and some brake cleaner washed through helps pardon things off.
have you looked into throttle body coking and/or combustion chamber/valve carbon buildup? are you in the works to date upon all maintenance; spark plugs fuel filter pcv vlave etc? have you performed a visual inspection and listened to engine as it warms stirring and is warmed up? oftentimes in engine take steps many factors may cause the same symptom(s)