>My manual 928 is just developing an engine problem. Two days ago I was
>startled when I couldn't get more than 3200 rpm. As I reach that rpm the
>engine bogs and will go no higher and I started to hear a hissing vacuum
>sort of a noise.
One thing to check on our early cars is the egr valve. If it leaks it can reduce engine power a lot. There are two vacuum hoses going to the egr valve. A red and an orange. The red comes from a thermostatic valve near the back of the right cyl head (under the air cleaner box). If you apply vacuum to that the egr should open and stall the engine. The orange hose comes from a vacuum amplifier (black round thing with about 4 hoses on it) If you apply vacuum to that it should keep the egr closed. If you disconnect the orange one only the engine will run very roughly when you press the accelerator. Maybe your orange hose is disconnected or the vacuum amplifier or egr are malfunctioning leading to the egr being open at times when it should be closed.
Other things to check out might be the valve for the charcoal canister for the gas tank fumes (big hoses on right passenger-side of the engine bay. Numerous hoses underneath plenum on intake manifold.
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