If the adjustment hole for the air/fuel mixture is left unplugged, you'll get a little unfiltered air into the system and maybe some dirt and dust. As I understand it, though, the unplugged hole will not affect the air/fuel mixture or the metered air because the adjustment hole is before the air metering device, i.e., the air sensor plate. That's how I understand it anyway. See what others say. I recommend plugging the hole somehow to keep dirt out.
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Thanks everyone for all the help, Doug C. 81 242 Brick Off Blocks, turbo bars and wheels, M46; 86 244, B230, 150k , auto; 81 242 Turbo, intercooled, M46, 122k.