Tuesday, September 8, 2009

The faulty adjuster unit causing a vacuum leak (E46 BMW)

The Problem:
Engine runs rough, to the point where it can cause the engine to stall out when idling idle or running at low RPM. The whole car shakes or shudders as the engine misfires every once in a while.

Characterized by the following codes (you might have a slightly different variety):
P0171 - System Too Lean (Bank 1)
P0174 - System Too Lean (Bank 2)
P0303 - Cylinder Misfire (Cylinder 3)
P0304 - Cylinder Misfire (Cylinder 4)
P0305 - Cylinder Misfire (Cylinder 3)

The culprit is a part that commonly goes bad on E46 machines, a little black box on the intake side of the engine called the adjuster unit. Mine went bad after 170k miles... yours may fail sooner. If you suspect it -- just change it out. Some people on e46fanatics.com re-glue the old part to fix the vacuum leak - but since the flapper inside the unit goes bad anyway (see video), I would highly recommend changing out the whole unit. The part should cost you just under $200 from the stealer (dealer).

Tools you'll need:
  • Torx T40 screwdriver.
  • 10mm socket and ratchet (an extension is useful here)
  • Pliers to pull pop out the plastic rivets used to hold down the air box
  • A T40 torx bit attached to a ratchet at a 90 degree angle for removing the bottom screw (see picture)

Time it'll take: 30 minutes if you don't drop any screws or tools/sockets into the engine compartment (Key here: TAKE YOUR TIME).

Diagram (Part #7 is what we're after)

M54 ENGINES (325 & 330)
07 ADJUSTER UNIT -- 11 61 7 544 805

Here's a video of the failed part and where it came from:

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