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Thanks aliboy, I should of mentioned that I have just replaced the turbo and exhaust housing and the rpm is steady. Plenty of power now. Supercharger cuts out at around 2500 as it should but with the problem I stated in initial post. i think the supercharger only works on rpm range and not boost pressure?Normally the supercharger coming in and out at 2800 - 3000 is because your turbo is not making enough boost. Are your rpm's fluctuating up and down a little at the same time? Need to put a boost gauge on to check, but most likely you need to get your turbo exhaust housing sleeved (if you have someone near you who does this) or get a new turbo. Welcome to the wonderful world of Volvo turbos. Other possibility is an intake system leak, but the bad turbo exhaust housing is a very common issue with Volvo's.