The check engine light on my 1993 300e 2.8 has been coming on lately. I have checked it by depressing the button in the box and come up with 5 blinks over and over. When I reset it the light stays off for varying amounts of time from minutes to days and then comes on always code 5. Does anyone know what that code indicates on my year and model?

Sticking EGR or plugged egr tube to intake/head.

Easy test is apply vac. at egr at idle.. If car runs rough with vac and smooths out when no vac. , the tube is clear and valve is working. [ make sure it SNAPS back when releasing vac.]

If all checks out , look for vac at the egr vac hose with a gauge.
[ You will have to gas it , as egr is not called for at idle.]
If no vac, check hoses to/from switchover valve in front of engine.
[under front cover.]

There was a EGR upgrade TSB, but check these first............