So I was working on the tie rods, took it out for a test and parked it next to the garage running. I noticed a hissing sound that would go away when I tapped on the brake.
So I popped the hood and couldn’t find any damaged lines.
Sound comes from behind the manifold kinda next to the valve.
Is that normal or is it stuck?
You may have to do a couple more tests, because where sound comes from can fool you.
In general if the sound changes when you step on the brake, it may have to do something with the brake booster, which uses the manifold vacuum.
So for example, when you step on the brake, outside air fills the “supply” chamber of the booster, and the diaphram moves toward the vacuum side, and amplifies the pressure on the brake. When you take your foot off the brake, vacuum is equalized in the two chambers and the diaphram goes back to the rest position.
So depending on whether the sound goes away while pressing or releasing the brake, the leak could be in different places.
I tap on the brake like 25% then for a second the sound goes away then it comes back. It’s mostly constant all the time.
Because the sound goes away when you press the brake pedal, I would start with the brake booster tests that are published in the manual in the section on brakes. If there is a leak between the brake booster vacuum chambers, or at the booster somewhere, one of the tests will fail.
After that you pretty much have to go from one vacuum connection to the next, one at a time, remove the hose at the connection to the intake manifold, cap the manifold connection or just hold something over it, until you find the line to the device that is leaking.
Or, you can spray starter fluid or something similar at one vacuum connection at a time, and listen for a change in engine sound when the fluid vapor is sucked into the intake through the one that is leaking.
I did a quick check and turns out it was the booster. A new one fixed that. Car was sitting for a full week and my battery died in the process so it sat longer. Now my idle valve is stuck and rpms sit 2k.
It’s getting old working on a 90s honda.