I seem to have trouble getting my 75 280Z running good. It all seems that the air flow meter is the cause of my problems. It blows black exaust back fires through the intack and has a lack of power. The hard part is the problem comes and goes. The other problem is that from time to time it also likes to hot . this problem also comes and goes. the last problem is the brakes. The brakes are very hard to operate. I have replacced every componet but the master vac. is this the problem or is something else.