Usually happens when the actuator spring becomes too weak to hold the wastegate shut, and it starts to open before the set amount of boost.
This means it takes longer to get on full boost because instead of all the exhaust gas going through the turbine, some of it is escaping out the wastegate instead.
The other problem that often gets mixed up with wastegate creep is boost creep.
Boost creep happens when the wastegate hole is literally too small to let enough gas out, the only other way it can go is through the turbine, which creates more boost.
This means it takes longer to get on full boost because instead of all the exhaust gas going through the turbine, some of it is escaping out the wastegate instead.
The other problem that often gets mixed up with wastegate creep is boost creep.
Boost creep happens when the wastegate hole is literally too small to let enough gas out, the only other way it can go is through the turbine, which creates more boost.