I have a 1985 230TE also. I have looked at many parts books and nobody ever list an oxygen sensor for the 230TE. What is odd though is that my 230TE with a late 1984 build date has a single wire oxygen sensor. I have been trying to also figure out this mystery because I need a new exhaust and everywhere I look the only exhaust available has no port for the oxygen sensor. If you are looking to see if you have a sensor or not then it would be a after the exhaust manifold and before the catalytic converter or first muffler. Depending if your version has 3 mufflers or two mufflers with a cat.
1985 230TE 5 speed.