What are these two little pipes?

1993 Audi 90S
Either side of the engine block, there are long, thin (I'd say 5mm) metal pipes that come from the back of the engine somewhere, to the
front, and stop. They're capped with tight fitting rubber stoppers.
Someone suggested they may be part of the EGR system?
The problem is, that I noticed the rubber stopper on the left side had cracked and falled away. When the engine was running, *very* hot air was being forced out of there. It smelt a little like exhaust.
I went to the local auto parts store, got a generic replacement and capped it off again, but a week later I saw that the cap I put on was gone too!
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Av wrote:

They might be O2 samplers for exhaust gas monitoring. If you have the 2.6 V6 you might have two exhaust headers to sample. Just a guess...
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