To check the vacuum first do a visual inspection of the pipe and hoses to the modulater. Next with the motor running attach a vacuum gauge to the hose at the vacuum modulater to verify full engine vacuum. To adjust line pressure you really should review the procedure in the service manual. It involves running the motor with a gauge attached at the line pressure port and turning the vacuum modulater to get the correct setting. This work is easy to do if you can get it on a lift but it is doable on a GOOD set of 4 jackstands. Always be extra careful working under the car especially with the motor running. David Teitelbaum vin 10757