Thanks Arthur. My next question was whether Code 13 indicated a O2 sensor fail.
I am suspicious of the EGR valve and pipe as it has never been cleaned out, its one of those maintenance issues I have been putting off for obvious reasons! If I suck on the vacuum line I can hear the diaphram opening and closing.
I am also suspicious of the changeover valve under the cover at the front of the engine but not sure on how to check it. The vacuum connectors are good and tight but do not know under what engine conditions the valve switches over?
As codes 36 and 39 are not showing I presume they can be faulty without registering to the diagnostics.

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1993 320E 140,000km