boost but I imagine because with the boost controller and the stock solenoid mixing one of them get confused and create more boost then needed. If you want to do a little test but be VERY careful you can plug it back in and watch what happens. I did it and with my boost controller off (pretty sure I had it off) and the solenoid plugged in, the boost would flux from 8-15psi. It was kind of weird but just unplugging it created a constant boost.