Boost controller

Solenoids may require small diameter restrictors be installed in the air control lines to limit airflow and even out the on/off nature of their operation.

Two-port solenoid bleed systems with a PID controller tend to be common on factory turbocharged cars.

For instance, a solenoid-type boost controller should direct all air to the wastegate when it is in the non-energized position (the common failure mode for a solenoid).

Designs which bleed off the intake air functioned similar to a blowoff valve, but on a constant basis to maintain the desired boost pressure.

These methods are rarely used in modern system due to the large sacrifices in efficiency, heat, and reliability.