Yes the power brake booster is controlled by vacuum as are 95% of them on light vehicles.

The vacuum pump is mounted at the front upper, drivers side of engine. A large line connects to it that goes to the brake booster with several nipples that provide vacuum to accessories such as shut off and vac locks and modulator if an automatic transmission.

Put a vacuum gauge on one of the nipples and see if you have vac with engine running. If not, break loose line at vac pump and see if you have vacuum from pump. Be careful, the fan is spinning very close to the pump.

If no vac from pump remove it. When you do, you will see a roller on the engine side of the pump that rides on an eccentric that is on the Injection Pump sprocket mechanism. That roller should be in good shape, smooth and solid. If not replace the entire pump, if the roller is okay, simply get a diaphragm kit and rebuild the pump.

If there IS vac at the pump then you need to start applying vacuum everywhere until you see where it does not hold vacuum and that is your leak.

Good luck,