Hi I purchased a 1997 Volvo 850 r about 6 months ago and I am having some issues with power loss when I am accellerating at full throttle and there is what sounds like a popping noise as well when you get on it like that. You can drive the car all day long with out this issue at half throttle and it is still a pretty quick car. (I have fallen in love with it! Lol) I boost about 18psi. The guy I purchased the car off of said it was just the turbo control valve that needed to be replaced. So I did so and with no change or result for the problem. Could it be the boost requlater? Or perhaps some fuel cut out, or vacum lines?
Aftermarket parts that I have are a full 3inch turbo back exhaust, short ram cold air intake, full racing suspension and the car has been lowered as well.
The car has 120,xxx miles on it.
Any ideas you have would be great!:)

 

Does it have a performance switch near the shifter? Is it set to S instead of E?

 

There is a switch that is for Economy Winter and Sport Mode. It doesn't make a difference which mode it is it when the problem occurs. I mean obviously I don't ride around in winter mode.

 

My car performs a lot different in E than S. When was the last time the PCV system was replaced? You may want to move this concern to the 850 section where 850 people can help you.