The plastic 'T' is actually the pcv device. The plumbing to the firewall side of it is at manifold vacuum, and all hoses need to be in good shape. Still, a vacuum leak would lean out the mixture, so I doubt if that is your problem. Running rich - at a guess - sounds like a sticking control plunger in the fuel distributor - not returning all the way to idle rest. Since I have never worked on one of these, hopefully you can get some more experienced advice.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7