Topic: p258b low power under boost/no boost.

[Rainbow Dash]

So I had a p258b. It went away, but. I am having low power while still in boost, like. before I could go up hills in 4th gear at 0psi, now i need 4-5 psi to go up the same hill in the same gear. I checked the brake booster one way valve, its not bad. I checked the evap purge solenoid, it is not bad, I have checked for vac leaks while the car is running, and found none. My car also chirps at 7psi+ from (what i think) is the High pressure Fuel Pump (but only when the car first sees boost, but is up to temp. so the first like 5 min of positive boost it will chirp). I am at a loss. I am very frustrated. Someone please please please help me. Car is stock except a K&N drop in filter and airbox mods. Those mods had already been done well before the issue.

[Rainbow Dash]

car is an 07 GXP btw. I guess I forgot to mention. has 124k miles, and was still on the OEM 41-102 plugs when i got it a few weeks ago

[Gentleman Jack]

Chirps?
What part of the car is chirping?

[Sol Asylum]

This code is for an electric vacuum pump used with the power brakes not having proper vacuum, not sure how it would have corrected itself and went away.

At any rate it should not be causing any low power or low boost issue.

I think you need to see if there are any new codes.