my engine

[steve75]

hi can anyone help i have a 318i e36 m40 bmw 93 ,its playing up ,when you drive normly the car is ok but if you try to go over 4000 rpm the car gos flat .so if im in 3rd gear (will do it in any gear )and go over 4000rpm it will go flat and stay flat till you let the rev go back down then it wll be ok till you get back up to 4000rpm .its had a full serice and a new rotor arm .it will only go flat at 4000rpm every time you hit it .has anyone had this prob ,as i said the runs fine till you hit 4000rpm