Intake vacuum leaks are some of the most frustrating leaks to troubleshoot.  Due to the airflow meter being the primary engine load sensor to the stock ECU, even small intake vacuum leaks can cause all kinds of headaches.  These can include, but limited to:  bad idle quality, low boost, hesitations, misfires.

Pic: Leak prone area: Description / Fix:
  Turbo Inlet Duct The rubber turbo inlet duct is prone to cracking, especially on the turbo side.  Check the clamps (there are several) for tightness and leaking.
  • Replace bad / loose clamps.
  • Replace TID if cracked.
  •   Wastegate Vacuum Hose This hose is not prone to failing unless it has been removed, but the metal fitting on the turbo compressor housing can get loose and pop off.  There are several clamps that hold the hose sections in place; check these connections for leaks.
  • Replace bad / loose clamps.
  • If metal fitting on turbo compressor housing is loose, metal epoxy is a quick fix.
  •   Splitter Pipe Zenki units are cast aluminum, while Kouki units are plastic.  Although failure of the Zenki cast units is rare, the Kouki plastic ones can crack.  There are a number of clamps and hoses that are connected to this pipe, so check all of clamps.  The hoses are originally reinforced rubber, so they do not fail that easily.

    The stock BOV / CBV attaches to this splitter pipe with another hose.  See below for more info.

    Of specific note, the BAC valve hose attaches to this pipe and is not clamped from the factory.  This hose regularly fails, especially with elevated boost.  We highly recommend to clamp this hose on both ends!
  • Replace bad / loose clamps.
  • Replace splitter pipe if cracked.
  • Clamp both ends of BAC valve hose.
  •   Intercooler Hoses Inlet and outlet hoses are reinforced rubber, so they rarely fail.  The clamps do go bad from constant removal.
  • Replace bad / loose clamps.
  •   Intercooler We serious doubt the intercooler is leaking unless under extreme circumstances.  The intercoler does have a couple fitting in the rear, passenger corner to a couple of bypass solenoids.
  • Replace bad / loose clamps.
  • If necessary, replace hoses.
  •   Throttle Body The throttle body inlet does have a triangle-shaped o-ring on it.  You can typically reuse this o-ring.  The outlet of the throttle body mated to a black plastic spacer and uses no gasket.  If the nuts are tightened to spec, there is very little leakage here.  If you do use some kinda gasket or sealer, be careful not to plug several vacuum holes in the black plastic spacer.
  • Replace o-ring if necessary.
  •   Upper Intake Manifold Major areas are the flange to lower intake manifold and several vacuum fittings.  Originally, Mazda used a paper gasket that seals the the upper intake manifold to the lower intake manifold.  Removal of the upper intake manifold is usually met with some resistance, as the Mazda paper gasket basically glues both flanges together.  With some gentle tapping with a hammer, the upper intake manifold should come loose.  The Mazda gasket typically stays in one piece on one of the flanges, so if it does, just use some silicone RTV for a better seal.  If the gasket comes apart, all of it has to be removed.

    Due to heat and age, the many vacuum hoses can go hard and loosen.  It's recommended to replace these hoses.  Silicone vacuum hoses are popular.
  • Replace upper intake manifold gasket.
  • Replace vacuum hoses.
  •   BAC Valve This has been mentioned in the Splitter Pipe area above.  This hose to the splitter pipe is not clamped from the factory, and we highly recommend you do so now.  If the hose is warped or cracked, replace the hose.
  • Clamp hose.
  • Replace hose if necessary.
  •   Blow-Off Valve /
    Compressor Bypass Valve
    The stock BOV connects to the splitter pipe and the TID.  Stock clamps are inferior single-wire type that can easily leak.
  • Replace clamps.
  • Replace hoses if necessary.
  •   Lower Intake Manifold Like the upper intake manifold, the lower intake manifold is similar.  The lower intake manifold seals the manifold to the engine itself.  Fuel and coolant leaks on top of the engine degrades this gasket, and eventually it will leak.  As with the upper intake manifold, there are several vacuum hoses on this manifold as well.
  • Replace vacuum hoses.
  •   Fuel Injectors What does the fuel injectors have to do with intake vacuum leaks?  Well, it is one of the most ignored areas when looking for leaks.  The lower rubber grommets on all injectors are used to seal the fuel injectors to the lower intake manifold (secondaries) or to the engine itself (primaries).  These lower rubber grommets harden and shrink quickly, so even new ones are prone to leaking within a few months.

    We've found out that 10mm I.D. silicone hose makes an excellent substitute.  A one-foot length of 10mm I.D. silicone hose can make like 20 of these grommets.  Using a sharp razor blade, cut a 3mm to 4mm section of hose that fits under each fuel injector.  The silicone hose will stay flexible longer in the engine heat.
  • Replace lower grommets.
  •   EGR Valve The EGR valve diaphram can tear and induce an intake vacuum leak.
  • Replace the EGR valve.

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