audi5kguy

I can't find my vacuum leak! My '86 S has a leak (I assume I do since removing the oil cap and dipstick don't impact it's idle)
Anyone have vacuum diagrams or some tips on where to start? This whole car is one big maze.

Also, would a leak cause it to stumble really bad when you hit the gas? If I hit it and hold it, it will die. I have to move the pedal all over the place to keep it going.

Will Ng

Check the main culprits....
1. crankcase ventilation hoses
2. vacuum brake boost hose (if so equipped)
3. charcoal cannister lines
4. if turbo, air shroud hose
5. HVAC/cruise control vacuum feed hoses (does the venting work correctly, cruise work?)

If the car runs w/ oil cap off, then someone has monkeyed with the car to allow it to maintain idle.
Check to make sure the air bleed screw at the TB is closed. I bet it's backed out quite a bit.
All vacuum is sourced at the intake manifold, just pinch off each line to detect which circuit contains the leak.

TonyOldSchool

and used talcum powder (in a plastic bag and a 1/4" hose attatched) to detect leaks. Not too much pressure! Also check those braided hoses, boy was I fooled, they "looked" good until I started this never ending EM job and I took off most hoses to find they (small dia. ones) leaked like sieve!

Will Ng

but it isn't talcum powder. I wouldn't recommend that clogging everthing.

The machine pumps in smoke at a mild pressure. Leaks are revealed as you see puffs of smoke exiting.
You can make one if you're handy. Take an aquarium air pump as your air pressure source. Plumb it to a heat safe glass jar containing some smoke producing burning material (newspaper, oiled rag, charcoal with some oil). Stick another hose from the jar lid to an intake manifold barb.

And of course, if you decide to try this, I claim no liable responsibility for the information put forth, as I am not a licensed or ASE mechanic or professional mechanical engineer. Lawyers required me to add that! :=)