Intermittent no idle... NO CODES!!

On my 97, well, my wife's actually, we've got an issue with the rig liking me & not her. Lately she hasn't been able to get it to idle, I thought it was the TPS but we fiddled with that & no luck. Played with the IAC & no luck. Here's what wierded me out: I got the thing to idle for me & then unplugged the TPS expecting it to do something, but no. Same with the IAC. We took it to Shmuck's while the check engine light was on & the only codes she got was D1, which they said is "manufacturer specific, and 18, which they said was "power trans" whatever that means. So they didn't help much. Just for fun we unplugged the IAC and TPS and then STARTED the thing, it runs fine......So, now I just feel dumb. Help anyone?