The vacuum line running from the Brake Power Booster is the most commonly used source for the Step 2 connection. This is the one source that doesn't cause the car to stall at idle speed when disconnected from the power booster. The vacuum in the booster is only needed when applying the brakes. On some vehicles, the PCV line entering the throttle diaphragm my be easier to get to but the engine would need to be set at higher RPM to offset the richer mixture entering the intake manifold. The kit that is used with the #2630 Step 2 is the same one contained in part #2610 Total Combustion System Clean-Up.