Hi.

So i got a aftermarket boost gauge in my s5 turbo with a vaccum side on it.

Goes from -1 bar to 0bar to +1,5bar.

At idle, i only get -0,5 bar vaccum.

I do have alot of truble at idle, low idle speed, and missfiring. And missfiring when i rev the engine and hold the rev in neurtal. When driving its better.

But what is normal vaccum at idle? And can low vaccum cause problems?

 

It should be in about the 15 to 20 inHg range, and 1 bar = 29.53 in Hg. So 0.5 bar = 14.8 inHg. Low vacuum is caused by vacuum leaks and/or low compression.

 

Compression is fine, iv checked it.

But if its a vaccumleak, then it has to be behind the throttlebody, right? Since the vaccum is messured at the dynamic chamber?

 

After the throttle plates is considered vacuum. And before the plates, but after the AFM is considered metered air. Vac leaks will decrease vacuum pressure, but metered air leaks shouldn't.

 

good info!