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      11-22-2012, 12:40 PM   #1
Imperator's Avatar

Drives: 2010 E92 335i
Join Date: Mar 2010
Location: Plano, Texas

iTrader: (8)

Does your brake booster hold vacuum with the engine off?

I've recently noticed a trend between cold starts where the brake booster has lost its vacuum and the brake pedal is stiff on the next cold start, where the car has rested for a few hours.

I'm thinking it used to hold vacuum overnight, even for 12 hours when I make the regular commute into work the next morning. My car is a 2010 E92 (Steptronic) with Cobb AP tune, ETS IC, iCarbon DPs and AFE S2 intake.

The car doesn't lose vacuum immediately after the engine is shut off but there must be some small leak in the system that drains the canisters over a few hours. This leak is not significant enough to trigger boost codes and the system holds vacuum well enough while the engine is running. I don't recall this difference after any of the mods were installed, though it is possible some hoses had to be removed and plugged back in.

This might also be normal behavior with the N54 as it ages but I figured I should ask around, see what others experience and get some pointers on what to look for.