Originally Posted by Junky_One
But if it's changing itself you'd think the problem would be under the dash, blend door perhaps?
Since it randomly changes itself, I'm leaning to it being a crack in the line at #8, not fully broken, just cracked.
The canister at number 8 is the vacuum reserve canister, its job is to maintain vacuum pressures to the hvac, cruise control while the engine load fluctuates, when there is a leak in the system it will cause erratic behaviors.
The faster the op runs the motor, the quicker they run out of vacuum pressure.