Check the hose clips for tightness and examine the trunking for any cracks or splits and plus every the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best mannerism to find a leak is to have the engine dispensation and hot and next spray lighter gas /propane or brake cleaner just about each joint in turn. If the engine rev s occurring you ve found your leak.
Its then worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a in poor health pump will all repercussion in insufficient fuel mammal delivered to the engine. Might after that be worth cleaning out the idle promptness manage motor / valve as these acquire clogged happening later carbon and some brake cleaner washed through helps clear things off.
have you looked into throttle body coking and/or combustion chamber/valve carbon buildup? are you happening 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 produce an effect many factors may cause the same symptom(s)