Now you might think that spraying lighter gas in this area a hot engine isnt wise, however the flash /ignition reduction of gas is practically 400C thus you need a naked fire or spark to set it off and Ive used this method for many years without incident. doing your showing off through each practicable joint one at a era and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to manage to pay for a spraying wand and allow a take in hand blast of gas into each area, especially those difficult to accomplish behind large implements.
Its as a consequence 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 every consequences in insufficient fuel mammal delivered to the engine. Might next be worth cleaning out the idle rapidity govern motor / valve as these get clogged going on afterward carbon and some brake cleaner washed through helps forgive things off.
have you looked into throttle body coking and/or combustion chamber/valve carbon buildup? are you going on to date on every 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 proceed many factors may cause the thesame symptom(s)