"Stuff" under the air-filter
 

Searching for a source of a vacuum leak I have come across the 2 controllers under the air-filter box (part#001 540 79 97). Even though they are located side/by/side, they react in a different way when tested with my MityVac. The bottom nipple and the one directly above it hold vacuum in one of them and in the other the bottom one does but not the one directly above it. In addition, there are two other nipples on the top "dish" that act the same on both. Does anyone know how to test them? Also, the newer version has only one nipple on the bottom and 2 on the top so it is not the same thing(must be some inline change that happened over last 20 years...). Appreciate any insights.

Model and year would be helpful for us to help you. I assume its the 87 300TD in your profile.

Ooops.... yes it is the '87 300TDT

Many people disable both of these, they are EGR and ARV, the 5-way connector in front of the cam cover can be replaced with a 3-way F connector.

Either that, or pull the two lines off leading to those, put a BB in each rubber fitting, and replace the line (blocking vacuum / airflow).

I may have to resign myself to that, but still would like to be able to test the two controls and know which one is bad.

bump
why are the bottom nipple and the one above it bridged?