Ok here's what I'm having, I'm thinking it's the the airflow sensor. I have a 91 volvo turbo. no check engine light as of yet, but when I'm on the gas and the rpm's gets to 5000 it's almost like the rev limiter kicks on and it it stops. the engine surges and shakes and the turbo boost gauge goes crazy. But the reason I'm thinking this is the airflow sensor is because it's dependent on the temp outside. the warmer it gets the sooner in the rpm band it'll do it