Originally Posted by weird beard

Car is a 1996 Volvo 850 GLT wagon. I am the twelfth owner, mileage is unknown, has had at least one engine replaced. This is a $450 beater I bought for the winter that has grown on me like a fungus. Car was seriously neglected before I got it.

Lately, since the temperature has dropped well below freezing, my 850 is lacking power under full boost. The boost gauge is reading high and the car seems to hesitate. I have hit the fuel cut a few times due to my turbo control valve sticking. Boost increases rapidly but the car does not accelerate accordingly. It actually accelerates when I start letting off the pedal and the boost drops (not hitting cut off). can't go full throttle on the freeway on ramp for example. Car has new plugs, wires, cap, rotor, maf sensor, front O2, air filter and fuel filter. No oil under the cap and rotor or the cam sensor. P0133 fault since I bought it, did not affect anything in warmer weather and I have changed the front O2 since. Believe that P0133 is actually the rear sensor since the Volvo fault for the rear will set the same P fault as the front. Passed a smog test six months ago (second try after basic tune up) Fuel economy has been dropping as well. All the parts listed were changed to rectify the problem, not prior to the problem. Rechecked the plugs, showing lean.

Thinking it may be fuel pressure related, but wanted some opinions before I try a pressure regulator. Possibly not increasing fuel pressure according to the boost and it's going lean? I have done all the basic checks I can think of except checking the fuel regulator for leaking. Also used only the recommended Volvo plugs and correct bosch O2 sensor. running shell 91 fuel. Car is bone stock.

thought I would try here as I have had luck with my Mercedes issues but nothing on the Volvo forums yet.