Vacuum leak FYI

**FastGpa** · 11-17-2017, 05:04 PM

So, a few weeks ago my 2001 530i started having some starting issues. It would take a few tries at cranking to start. Also, the brake pedal (booster) "felt" different occasionally when driving. It has 190,000 miles on it, so I was pretty certain it was a vacuum leak somewhere causing my issues. I had recently replaced my upper rubber boot behind the MAF. I inspected the lower rubber boot at the time and it was fine. I suspected that might be my source. Took off the airbox (replaced filter with a new Mahn unit), the MAF (cleaned with with MAF cleaner), and the upper boot. Inspected the lower boot...no issues. Inspected the vacuum lines that T off the upper boot...all fine. Took off the driver's side cabin filter unit and inspected the brake booster vacuum line...all good.

So I grabbed a bright light...knelt down next to the driver's side fender, and began inspecting all the hoses and connections on the intake manifold. I had previously zip-tied the DESA valve connection tight when I rebuilt the DESA valve, and that had come off. Repaired that...kept looking. What I found is in the picture below. As you kneel at the driver's fender, and scan under the intake for issues, there's a nipple on the far right under-side of the intake manifold right next to where the brake booster vacuum line goes. Mine was capped with what looks like a factory cap. HOWEVER....that cap had gotten brittle and cracked...allowing for a leak. I repaired it with a short hose with a bolt tightly stuck in it and clamped (I know I know...).

Car started right up. Brake pedal feel was proper.

So...just another quick and easy piece to check if you're having any vacuum associated driving issues...
CD1A4A08-A61B-4F8A-81EB-9D283A1500D3.jpg

**RuskiE39** · 11-17-2017, 09:48 PM

Nice find, its however, called DISA

**edjack** · 11-17-2017, 10:31 PM

Congrats!

**djb2** · 11-18-2017, 01:35 AM

Based on my boneyard surveys, this is a very common problem.
I never find a large cap in good condition, and many have split the entire length.

There are three vacuum ports on the manifold at the aft end. Typically two are capped and the third is used for the secondary air valve control. The large cap is usually in worse condition than the small.

A reasonable short-term fix is putting some gasket sealer on the crack and external surface, then immediately shrinking large diameter heat shrink tubing over it.