Poor Idle after Exhaust Overhaul

[Bman]

This weekend I put in a new (used) exhaust system on my 84 Doka which has a 2.1 Block and 1.9 FI system. From the factory this Doka was a diesel, but POs have altered things so much that I never know completely what I'm going to need for a job. Case in point, the existing exhaust on the engine was an air-cooled 1-2 and 3-4 cylinder pipe setup, with a low hanging EMPI muffler. Luckily all nuts and double threaded bolts came right off (but one) and I was able to put the used 2.1 pipes on correctly with new hardware and gaskets. I opted NOT to use any donut gasket after the elbow pipe. I also put on a used Catalytic Converter, some of the honey comb was missing, but there was NO rattling in the thing. The used exhaust system I got included a used 2.1 muffler, however with the cat and the lack of adequate hanging points (I have a rear engine tin which blocks the rubber engine mount on the mustache bar) that muffler was too big to fit into the area, so I had to steal the 1.9 muffler off of my 89 Westy with a Ticco engine. That all fit fine and the motor sounds a lot quieter.

My question is that after short drives (2-7 miles) around town, when I am warmed up and arriving at my destination, the engine is idling poorly (approximately 300rpms) until it quits all together. A few thoughts, the outlets on the 2.1 piping is all 2", so the outlet from the Cat is 2", but the inlet for the 1.9 muffler is 1.75"; does this create enough of a back pressure to choke the engine?

Here in OR we do not need CATs, however I like the thought of a cleaner exhaust, could this used CAT be choking the engine? Also the CAT on this system was the only place I could connect the O2 sensor to.

Could the O2 sensor be the problem? In my haste I did not label the connection when I disengaged to remove. Does the O2 sensor wire connect to a green wire that originates from within the engine wire harness?

Thanks for any tips and thoughts you may have.
_________________
~Bryan
1990 Burgandy Tintop (Wife's Daily Driver)
1989 Tiico Westfalia "Taj"




2WD Doka build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=503578&highlight=
FaceHook:
https://www.facebook.com/pages/VW-T3-DokaSinka/129026087217120?ref=hl

[Bman]

Using the search and I'm beginning to think this is an Oxygen Sensor issue. I have a ONE wire O2 sensor, and even in my confusion above, there is only one possible green wire that it could have originally been connected to. So at lunch I unplugged the oxygen sensor and did a few mile trip with one stop, not sure I got it hot enough, but I didn't have extremely sluggish idles. It still is idling about 5-600rpm, a full bar and a half below the 1K range.

I'll try this unplugged condition on the way home tonight and see if there is any change.
_________________
~Bryan
1990 Burgandy Tintop (Wife's Daily Driver)
1989 Tiico Westfalia "Taj"




2WD Doka build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=503578&highlight=
FaceHook:
https://www.facebook.com/pages/VW-T3-DokaSinka/129026087217120?ref=hl