It called a LAMBDA probe or sensor in some countries and on some makes/models. It's called and O2 or Oxygen sensor in other countries. 85 325e should call it an oxygen sensor. As discovered in an earlier thread the 316 calls it a LAMBDA. Does the same thing, compares oxygen levels in the exhaust stream with oxygen levels in the atmosphere and then sends that info to the computer which determines fuel trim. Or is it a different part? can you reference the number in the diagram Jarda posted?