Engine Performance problem
2000 BMW 740 V8 Two Wheel Drive Automatic 120000 miles
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Start hearing a loud squealing noise which i thought was a dry belt. noise only starts if I accellerate and stops if i give the pedal a quick hit but after a few days it didnt get better and when this noise appears the vehicle runs rough and tries surging forward. Last time noise started i stopped and looked under the hood and cldnt tell where the noise was coming from so i decided to take the oil cap off and when i did noise instantly stopped and car ran smooth, when i put cap back on noise started again....also when taking cap of it seemed like it was under a lot of pressure.

When was the last time the PCV was changed?

I agree with Merlin. There is a plate on the rear of the intake manifold that is the PCV and it can be accessed without removing the manifold IF you are careful removing the bolts as they are T-30 TORX and can easily be stripped. If the manifold does need to come off you should replace the valley pan too as this is a preventive maintenance item as well as the intake manifold gaskets. Repost if you need help with this job and I will assist you.