finding vacuum leak

[dmma163]

On my 1995 911, I have avacuum leak, as evidenced by surging at start up, and the fact that removing the oil filler cap makes no change in idle speed. Having looked at hoses in the easy places, what pieces should I remove first to try to locate the leak? Also, if anyone has a recommended carb cleaner spray that works well for this purpose, I would be interested (the one I currently have apparently is not volatile enough to make much change in engine rpm, even when spraying directly into air box).

thanks.

[twistoffat]

be careful with Carb Cleaner as its flammable. Check your hose orings etc visually first.
You might get lucky

[Zeke]

Using WD 40 (also highly flammable) is good for sealed surfaces like manifold to head. But if it's a cracked hose, the spray method is less effective.

[86 911 Targa]

Some one posted the use of propane? to find a vacuum leak.

[Joe Bob]

Some use low flow propane gas....unlit of course.

[efhughes3]

Starting fluid works too

[jrumiano]

Just a hint, I had the same problem, my 85 had several intake manifold gaskets with missing pieces, which I assumed got sucked into the engine over the years. this was the root of my vacuum leak problems. I ended up taking off the entire intake manifold and removed / cleaned the remaining gaskets from the heads and manifold, as well as lightly sanding the spacers flat on a piece of plate glass with 220 grit paper. Did the trick for my surging idle problem.

Good luck.

[rusnak]

Starting fluid (ether) is what I use. Buy two cans at least. Vacuum leaks are tricky to find. You may need a whole bag of tricks, including the refrigerator hose trick (stick one end in ear, listen with other end).

[pete3799]

I think i read on here (Pelican) that the idle doesn't change when removing the oil cap on
the newer cars. I might be mistaken on this.........anyone?

[jrumiano]

Pete,
Nope that's incorrect information. When the oil cap is removed on the newer (84 - 89 3.2L) the engine idle speed should drop. If if doesn't, that's a sure sigh that there is a vacuum leak.

John

[efhughes3]

Uh, the original question refers to a '95. Hence the comment on the other post about "newer". Personally, I do not know if a 993 drops idle.

Pete,

Nope that's incorrect information. When the oil cap is removed on the newer (84 - 89 3.2L) the engine idle speed should drop. If if doesn't, that's a sure sigh that there is a vacuum leak.



John

[jrumiano]

My bad, I misread it as a 1985 not a 1995.

[scarceller]

Propane works very well but you need to get close to the leak. Starting fluid is much more effective as it seems to find the leaks very easily and you can see where your spraying it.

With that said: the very best way to find any and all leaks is with smoke machines. Many pro tuner shops have these as well as some of the better dealers and mechanics. This machine attaches to the intake with engine off. It then starts to fill the intake with smoke and it will find every leak in minutes! I had my intake done this way few years back, you can even see smoke around the throttle plate shaft! Simply amazing.

Ask around to see if someone in your area has such a machine.

[Vincent Hill]

I am in the WD40 and Carb spray camp because the starting fluid actually enters the air and raises the rpm when you are not at the leak after spraying around for a while. I replaced my Airbox and a few other things and found that even Paint with a straw on the Nozzle is great, Because when you take it apart you can see the evidence of exactly where the paint went!

I saw it in the Airbox, Plastic injector 0 rings and the runner gaskets!

[1990C4S]

Originally Posted by scarceller

the very best way to find any and all leaks is with smoke machines.

You can pressurize the intake to 3-5 psi and squirt soapy water around. Cheap and safe. And fast.

Poor mans smoke machine.