I can't explain the function of the check valve but it would make sense that it would either keep it closed or open at all times if you have it in place. My system doesn't have it, though I am not even sure my EGR works. The vacuum to my air pump is disconnected atm.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.