87 b2200 exhaust to intake/check engine? (pic)

Hello fellow b-series enthusiasts. I recently acquired a carbureted 1987 b2200, the engine was rebuilt under 1000 miles ago and the interior restored and I'm planning some restoration on the exterior to really make it perfect!
However I am facing one somewhat strange issue with it
Let me preface by saying that for the most part it runs really well super smooth idle and it just feels good on the road.

Under the hood I WAS missing a hose that connects from the exhaust pipe to the air cleaner (see pic)

I noticed that when the vehicle is running exhaust fumes pour out of the exhaust side (who knew?) and will leak into the cab filling it with the wonderful smell of exhaust. I went to my local parts store and got a hose to plug it up as you can see in the pic and although now it's not spewing exhaust into the hood/cab while I'm driving it's started running pretty poorly with really no power at all and the check engine light coming on and off every so often. I'm not sure what the source of the problem is as the truck is barely drivable with the tube on, and fairly unpleasant to drive with it off with all the exhaust coming to the cab

Any thoughts on what the problem could be, I thought perhaps the previous owner had plugged the air cleaner side and thats why it was affecting it so poorly but I checked and it was clear straight through

Thanks a million,
Jim

Your catalytic convertors plugged.

I think the valve that controls the exhaust flow is stuck - quick fix would be to plug that hose.