Just did a rebuild and have run the car in.. it runs fine.. except for the idle vaccums is low.. at 900 rpms the vaccum is -6 psi i think 300 mmhg ....

Its just that after a run the idle drops to 750rpms and the vaccums drop to -4 psi or 200 mmhg.. I am confused.. also the car is running rich all around...

But it feels really fast.. and the exhuast pressure coming out of the exhuast at idle is too much.. i can stand like 4-5 feet away from the car and feel the pressure...

Sometimes after i take a full boost run and then turn off the car and then after 5-10 mins turn it on .. there is a lot of black smoke from the exhuast and it starts like a V8 and then after 1 minute of idling becomes ok..

there is slight shaking too in the engine at idle..

what can it be?

thanks