To add to Mike's comprehensive summary I would also look at the vacuum check valves (blue/black, green/black on later models) near the firewall under the hood. These prevent the vacuum in the reservoir and other devices from bleeding back into the intake circuit--you should be able to suck on them one way but not the other.

The large check valves in the line to the brake booster and in the vacuum pump itself occasionally go bad. The diaphragm in the vacuum pump frequently fails, completely compromising vacuum in the crankcase--if that's the case you'll see oil smoke on the overrun as oil mist is drawn into the intake and burned.

These vacuum leaks are often tough to find--good luck


Tim Kraakevik
kraakevik@voyager.net