I had a hissing noise in my rig a while back whenever I pressed the brake pedal while stopped with the vehicle running. Long story, but I ended up changing the brake booster.


https://www.yotatech.com/forums/f116...-issue-237555/

and Toyota's $2,600 "suggestion" on fixing my issue:

https://www.yotatech.com/forums/f116...topped-207998/

The hissing is gone, and the brakes work, though they don't feel great. They stop the truck, so maybe I'm just too used to driving my much newer, lighter car with 4 wheel ABS disc brakes the last 3 years. My 4Runner is only used once a week or so since I bought a car, so I don't really remember how well the brakes worked years ago.

I got the oil changed in the 4Runner this week, and the mechanic said he heard a vacuum leak somewhere, but could not pinpoint it. Moving the hose from the air intake box made the truck almost die, he said.

So, how do I test for vacuum leaks? I searched the forum, but just saw several people recommending such leaks be found to improve fuel mileage, etc., but they never specify how to check for the leaks. The mechanic said my MPG would probably improve if I fix the leak.

BTW, replacing the brake booster is a PITA. Stock up on booze and prepare to throw a tool or 7 while cussing at the truck if you try it.

 

Get a can of starting fluid and judiciously spray the vacuum hoses. When the idle changes, you will have found your leak.

 

I'm told an unlit propane torch will also work.

Remember that both of these are very flammable. Don't overlook the word "judiciously."

 

Bottle of soapy water is good too!

 

Wouldn't vacuum suck in, so that any bubbles created would be inside? How would you see them?

 

I use carb cleaner with the straw attached. Spray anywhere that air passes through, AFTER the AFM. (NEVER spray before the AFM!)

Spray around all vacuum hoses where they begin and terminate, and also along their entire length. Spray at the intake manifold gaskets, the injector grommets, around the EGR and associated gaskets, throttle body. When you hear your idle jump, you've found your leak.

It works WAY better than an unlit propane torch because it has force behind the spray and the engine fan(s) don't blow it away easily. Plus, you can actually see where it's going.

 

pull out one of the vacuum hoses you think the sound is coming from smoke a cigar and blow some smoke in it and where ever the smokes comes out theres your leak.

 

that won't work. same principal as the soapy water. We're checking engine vaccum leaks, not pressure leaks.

 

Here is a you tube video, I've been looking for the same thing.


http://m.youtube.com/#/watch?v=mYa8rcHeN3A&desktop_uri=%2Fwatch%3Fv%3DmYa8rcHeN3A