hey i have a 99 civic si and i notice my car bogs before 4k rpm, once it hits 4k though it gets full power. when i turn on a/c, it gets even worse as if i lost 100 HP.

i recently did a tune up accept for the spark plugs which i have no idea how long they been on there since i bought the car about a year 1/2 ago.

my car has 125k miles

whats wrong with it?

 

did you do the 100k tune up? also, how hard has the vehicle been driven? have you checked the compression in each cylinder lately? maybe its time for a minor rebuild? or a b18 :D