Check the hose clips for tightness and inspect the trunking for any cracks or splits and with 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 running and warm and subsequently spray can lighter gas /propane or brake cleaner just about each joint in turn. If the engine rev s going on you ve found your leak.
Its next worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a below par pump will all result in insufficient fuel beast delivered to the engine. Might next be worth cleaning out the idle speed control motor / valve as these get clogged occurring gone 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 in the works 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 perform many factors may cause the similar symptom(s)