1991 240 - Engine Light on, 6 codes!

Hey everyone,

I'm helping a friend who has a '91 240 sedan. It's running without any real issues, no stalling or issues starting. It is getting pretty poor fuel mileage (13mpg) and is very sluggish. The engine light came on recently and it's now reading 6 codes:

2-3-2 (rich/lean mixture)
1-1-3 (lambda ctrl - too rich/lean)
2-3-1 (lambda ctrl - too rich/lean at partial load)
2-2-1 (lambda ctrl - too lean at partial load)
1-2-3 (coolant temp sensor missing/faulty)

EZK - 2-4-1 (EGR system flow too low)

In researching the codes above, I'm being thrown in all sorts of directions - oxygen sensor, AMM, ECT sensor, vacuum leak, etc. I'm not sure what I should test first or if the above codes would point to any particular issue.

Any insights?
 
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