93 Mazda 626 CEL code?

I don't see an "18" either. Are you sure it isn't a code 9, (coolant temp sensor signal out of range)? FWIW, the first thing I thought was that 18 was a fuel mixture type of code, as it is the next number after the famous code 17, but upon checking my sources it doesn't appear...

I would double check for a code 9 and if it *is* your code, troubleshoot the ECT sensor/wiring. If the fault is intermittent, verify the wiring from ECM to ECT is OK with ohm meter plus wiggle testing, verify the female terminals in the ECT connector are tight and corrosion free, then replace the ECT sensor; they can experience an intermittent internal open circuit that will set code 9.

Toyota MDT in MO

We figured out what it was... It was a 10 and an 8. :)

I had forgotten to connect the MAF sensor about a month ago for a few minutes while cleaning my throttle body.

Thanks!

Good for you. In retrospect, I feel like a dumbass for not thinking of that possibility. It's extremely common for someone to leave the MAF conector off after air filter or throttle service. Those two codes will set within one second of the ignition key being turned to "run".

Toyota MDT in MO