ka24e problem need help!!!

[Harvey s13]

i have a 1990 240sx with a ka24e. about a month ago every time i got it around 5000 rpm's it would start running bad the rest of the time after that even when rpms were low. now, about two weeks after that, it runs like it did when i got it at high rpms but it happens rite when it starts and always runs like that. it runs like it has a major miss or a real bad vaccum leak, but ive checked all the vaccum lines & their all good, & i put new plugs and wires on and it still runs the same.

any help would be great, thanks