92 190E 2.3 4 cylinder hesitates by acceleration

[Mauidieselpetr]

my friends benz died on them few times, then started again and brought them home....starts after 1 or 2 secons, but with difficulties...idles allmost perfectly...when you hit gas, hesitates for half second, than revs up....
i've checked distributor, cables,plugs, all good...
performed fuel pump volume test..as factory manual says...shoots enough fuell, fuell pressure past pressure regulator was 40 psi...when i poured tiny bit of catched fuel in intake, car started immediatelly and ran perfectly for short time....
regarding to factory manual for any other tests i need special tools which i don't have, so i.m hoping that you know some other steps to locate the problem...
thanks all of you for help
petr