This could be an airleak after the airflow meter, any let breathe dragged in here isn t seen by the ECU and correspondingly not compensated for and can thin the engine out and can along with permit the engine to rev occurring considering not desired causing harsh running. As its a mechanical anomaly it tends not to approach upon the irregularity open and you can sometimes hear a hissing noise like the engine running.
Its with 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 repercussion in insufficient fuel mammal delivered to the engine. Might with be worth cleaning out the idle rapidity rule motor / valve as these get clogged going on as soon as carbon and some brake cleaner washed through helps free things off.
have you looked into throttle body coking and/or combustion chamber/valve carbon buildup? are you going on to date upon every maintenance; spark plugs fuel filter pcv vlave etc? have you performed a visual inspection and listened to engine as it warms going on and is warmed up? oftentimes in engine take steps many factors may cause the same symptom(s)