I'd appreciate anyone identifying this for me and telling me what it does. I was going to Seafoam the manifold by introducing it via the vacuum hose of the brake booster but saw this between the hard line from the TBI base and the port on the booster. I figured that I probably shouldn't pour the Seafoam thru it; at least until I knew what it was, what it did and whether the additive would harm it. This is an '89 R1500 5.7L disc/drum. I looked at the vacuum routing sticker on the 'burb and at the routing schematic in the Chilton #28624 manual but didn't see anything or these old eyes missed it. It's the small split case cylinder between the booster and the air cleaner. Appreciate the help, Thanks.