So I have reached an impasse. A couple weeks ago the brake booster on my 1995 SR failed and I got a suitable replacement swapped in without too much issue. A few days later, the truck dies on my wife, and when I re-start it, I hear a very clear vacuum leak. Nice loud hiss, but strangely hard to locate by sound. Spraying the various sprays under the hood has resulted in mixed results at best....

Here's where I am at. As best I can tell, the leak must be somewhere near the TB, but not AT the TB. It seems to be closer to the firewall, and possibly even under the intake plenum. I have felt every line I can as far back as I can and still have I come up empty. I have tried to look for anything helpful at all and I am still coming up short. What I do know is that the truck has trouble running at idle, and if I haven't stepped on the brakes in a while, it's like it needs to build up vacuum a bit before the booster really kicks in.

Any ideas on what is my most likely culprit is? Please tell me I don't have to remove the plenum, I really don't want to.....

Most likely the last thing you worked on. Those booster lines can get very brittle. Also check the bottom of the main intake tubes as well as the baffles on the intake tubes.

That was my thought too, but I have traced the whole line from brake booster to the intake plenum and have no breaks or leaks in it. Based on where it sounds like the sucking is coming from, it does not explain it. I am not 100% sure what you mean by the bottom and baffles of the intake tubes... do you mean I should remove the whole intake? I know I might have to, but I really don't want to!

I mean the ribbed rubber main intake tube.


As far as removing the upper intake, there's not much under there but it's worth a check 20-30 minutes.