I have a 1991 240 Base w/ EGR -- recently had some problems wherein my ECU seems to be kaput. It was a -933 (with EGR) and I replaced it with a -951 (no EGR) because it was cheap (ebay), etc...

So since my ECU won't be activating my EGR, it should technically remain closed, and not recirculate exhaust gas, correct? I've read that this can cause detonation, but I'm curious what you guys think. Many of these 240s don't have an EGR -- since mine does, but it's not being used, is it more likely to develop problems? I've been driving it for about a month with this ECU, and haven't noticed any problems.

Should I try getting a -933 ECU again, or is it a non-issue?

Thanks for your insights!