You can reset the OBDII codes with your code reader, can't you ? I don't think it will go into "limp" mode unless there are certain OBDII codes set. In fact, I'm not so sure the D1has a "limp" mode. After you reset the codes it takes a certain drive cycle to get the code to go from P1000 (test cycle not completed) to P1111 meaning that the cycle has completed. Neither one of these codes will set the light on (CEL).

So far I've replaced/repaired : ECU, MAF, TPS, and IAC sensors, checked for any vacuum leaks, checked fuel pressure, checked sparkplug wire resistances, checked sparkplug gap and carbon buildup, battery voltage is normal (so alternator isn't a probable cause? )....
I think I'm going to end up crazy if this doesn't begin to show signs of repair with all the money it's absorbed.

Does anyone have any theories as to what would cause a poor idle ( will not maintain ~800 rpm ever and will stall if rpm drops ) and some trouble at high speeds with the rpms dropping and then returning to normal??

Thanks in advance,
Towne