The 3 most common areas for intake leaks on your vehicle are:
-the intake boot at the throttle body, the elbow that comes off the boot to go to the idle motor rips. If you feel around the boot, you would be able to stick your finger in the elbow if it is ripped.
-the crankcase vent valve or hoses. The hoses are known to deteriorate, especially the lower hose from the valve to the dipstick tube. These can be visually checked by removing the airbox and intake tubes to the throttle, but you can usually use throttle body cleaner sprayed lightly down in that area under the intake manifold and see if the engine races up
-the DISA valve, bolted to the side of the intake manifold, above the throttle body. It had an electrical connector to it, and a plastic rod to a vacuum diaphragm. Again if you spray throttle body/carb cleaner in the area of where the actuator rod enters the diaphragm, the engine will race up if it is leaking.
Hope this helps, please use the accept button as this is the only way I receive credit for my work.
The intake manifold adjusting valve is the DISA valve that I described above. The only other item that I have seen on these engines cause a lean trouble code is the oil filler cap leaking because the seal is worn.
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