Factory boost control relies on a flimsy, inefficient solenoid. When boost levels are increased over stock, the factory actuators fail to properly meter boost. The resulting spikes, dips and erratic response can damage your engine and spoil the performance gains. An upgraded electronic boost control solenoid allows a much lower waste gate duty cycle to produce higher boost levels giving tuners better control and decreasing spool time. Now lets discuss why.

Stock 2-Port Operation
The stock solenoid is part of the stock bleed-based boost control system. When the solenoid is off (closed), pressurized air from the compressor is fed straight into the wastegate control. Any increase in compressor pressure beyond the rated pressure of the wastegate control results in the wastegate being opened, preventing buildup of boost.
When energized (opened), air is allowed to bleed off the compressor-to-wastegate line by way of a “T” connector. This prevents the wastegate from seeing the full compressor pressure, allowing boost to build. Most model years include a restrictor pill in the hose connecting the compressor to the “T” which meters the air for the stock ECU calibration.
While the stock system operates adequately, it can lead to problems at higher-than-stock boost levels. Since the bleed system is sized for the stock turbo at stock boost levels, it is typically incapable of correctly metering air at higher boost, allowing the wastegate to see pressure and open before intended.
Additionally, since the wastegate is never completely cut off from seeing compressor pressure, it can open at low boost levels and inhibit boost buildup. Ideally, the wastegate should remain entirely closed for fastest boost buildup (as all exhaust is then forced through the turbine).

Aftermarket 3-Port Operation
A 3-port solenoid does away with the bleed-based system, explicitly shunting air from the compressor to the wastegate, or compressor to vent (or back into the intake post-MAF, OEM-style). Drawbacks of the bleed-based system are thus eliminated, with the wastegate seeing literally no pressure when the solenoid is energized, to seeing all of the compressor pressure when the solenoid is de-energized.
Now able to totally control the opening and closing of the wastegate, the ECU is able to control boost with greater precision and reduced response time.

This modification will make your current boost map OBSOLETE. You MUST retune boost. If you have no way to tune your boost control tables, you should NOT do this mod.

There are a lot of options out there. Some are a little easier to install than others, but all perform the same function. I have done some research in the solenoids available. If you do a little looking around you can find reviews for each of them