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Braking issues and engine idle speed

Jun 6, 2023
I’ve had issues pertaining to my brake pressure recently that seems to be directly affected by the cars engine speed. Playing hand in hand, the cars idle is affected when I press the brake pedal.

First issue: On a cold start, if I press and depress the brake pedal, the cars idle speed with fluctuate mildly with the pedal movement. Even when the car is warm in Neutral or Park, pressing the pedal with cause a drop in RPMs. Is this normal?

Second issue: The cars stopping power and brake pedal travel fluctuates depending on speed and RPMs. If I accelerate and quickly press the brake, there is a lot of pressure. If I am idling along in a high gear, coasting down a hill for example, the travel of the pedal is long.

The car (1992 Volvo 240 B230F sedan) recently had the brake system flushed. There is 100% new fluid in the lines and in the reservoir. The reservoir recently had the grommets/seals replaced. All lines are in healthy, damage free condition. Rotors and pads are within normal limits.

Any suggestions or thoughts would be appreciated!
Yes, the check valve is just pushed into the rubber seal on the booster. Use some silicone spray lubricant on the seal so that it will come out without tearing the seal. There are barbs on the check valve that will make it difficult to remove so wiggle it back and forth while pulling gently so as not to break the plastic valve.
I have inspected the check valve and everything appears to be functioning properly. Any other recommendations of areas to check/service? How can I tell if the entire brake booster is failing?
Do you hear a wooshing noise inside the car when you step on the pedal? It could be a bad diaphragm in the booster.
When I step on the pedal it sounds like I’m pumping up a basketball. So, yes!

Is this fixable or do I need a whole new booster?
Having just replaced the booster on my '88 740t, the most difficult part was getting the pin back in the brake pedal arm connecting the booster plunger. I installed the booster and realized it needed to be loose which made it easier to align the pin in the hole, so I loosened the bolts almost all the way. It took me a bit to figure that out.