Check for intake leaks

From BMW E34 Encyclopedia


Air leaks cause pressure loss within the intake manifold/unmetered air to enter the system.


  • Inspect rubber intake boot (take it off and inspect all seams within the flexible part of the boot for any holes/cracks).
  • Make sure you have rubber spacers on ICV and intake boot they go under the plastic where claps connect.
  • Inspect check valve within brake booster.
  • Inspect PCV plate in the rear for missing fittings, obvious signs of air sucking your hand in where plate mates with intake manifold.
  • Inspect area where throttle body mates with intake manifold.

John Doe propane test[edit]

  • Purchase hand held propane, turn it on (do not light it!) and let propane gas around areas where you suspect an intake leak. Your idle will change if leak

is confirmed.

Professional test[edit]

  • Use a professional smoke machine to pressurize and smoke the intake. This is the best and most straight forward way. Usual charge is $100/per test.