My 91 245 has developed a whistling noise around the intake/vacuum hose/fuel injector area at idle. I cannot find the exact cause. If i remove vacuum hoses it drops the idle enough to make it stop, as soon as you raise the RPMs it stops. While driving, no matter the speed, as soon as I let off the pedal it starts. Any ideas? Could this be an intake manifold gasket? Any help is much appreciated.

If in fact it is a vacuum leak you might have better luck probing for it with a stethoscope or just listening through a long piece of hose, another approach is to squirt water around the precise areas with a small water bottle and listen for the idle to change. A vacuum gauge is a handy tool to let you know if there is a leak but listening or spraying is probably the fastest way to locate the leak. One common loud leaker is the hose that leads to the heater controls.