1994 E320 CEL
 

Hello all,

My mothers E320 has a CEL again. Last time it was thought to be a throttle body and we replaced it (the wiring was deteriorated).

It has since come back on twice, but only while the car is decently warm. Both times it has come on has been while it was sitting at idle for 10-15 minutes. I checked the codes and it blinks 5 times which points to an EGR issue.

Anyone have any ideas on where to start? 02 sensor maybe?

If the code blinks EGR could that not be interpreted to mean that something in the EGR system has gone wrong? Changing the O2 sensor is great of you need to do it, but it won't clear your EGR code. You have already been pointed in the right direction by your onboard computer.
It's either the EGR valve, or the EGR tube is clogged and needs a cleanout. The former's expensive, and the latter's very difficult to access.