Here are some possible causes of your 1990 Buick Park Avenue cutting off when you press the brakes:
1. Brake booster problem: If your car cuts off when you press on the brakes, it may be due to a problem with your brake booster. The brake booster is a device that helps increase the amount of force applied to the master cylinder when you press the brake pedal. If the brake booster is not working properly, it may not be able to provide enough vacuum to the master cylinder which can cause the engine to stall.
2. Idle air control (IAC) valve issues: The IAC valve controls the amount of air that flows into the engine at idle, helping maintain the proper idle speed. When you apply brakes, the IAC valve is supposed to compensate and increase idle speed. If it fails to adjust, the engine can stall.
3. Faulty ignition switch or wiring:
A faulty ignition switch or problems with the wiring connected to it could cause intermittent power loss when pressing the brakes. The ignition switch cuts the engine's power when turned off, and if it malfunctions, it may also disrupt power when braking due to the added electrical load.
4. Electrical issues: A loose or faulty connection in the electrical system, particularly in the wiring related to the brakes or engine controls, could cause the engine to cut off when the brake lights or other electrical components activate.
5. Vacuum leaks: Vacuum leaks can disrupt the proper functioning of various systems, including the fuel and emissions systems. If there is a significant leak, it could lead to a decrease in engine vacuum, impacting the fuel mixture, idle speed, and potentially causing stalling when the brake pedal is pressed.
6. Faulty fuel system components: While you mentioned that the fuel pump and filter were replaced, there may be other issues within the fuel system. Problems with the fuel pressure regulator, fuel injectors, or even a clogged fuel line can cause the engine to stall or run erratically.
7. Transmission problems: In some cases, transmission issues, such as a faulty torque converter or a problem with the transmission control module (TCM), can lead to issues where the engine cuts off when braking.
Solution:
1. Check the connections of all the hoses going into the break servo.
2. Next check vacuum lines for any leaks from the engine to servo.
3. Check your brake pads.
