This mis fire codes had to be eliminated first, which you did. It may not feel like you accomplished anything, but you did. This is part of the fun of auto repair.
It is not typical to have a high engine load at idle as you describe. However that is one of the symptoms of the problem that is happening.
Conditions to set the code po507 include:
-vehicle speed at zero mph
-tpangle at zero %.
-BARO is greater than 70 kPa.
-Ignition voltage is 9-18 volts.
-IAT is greater than -13degrees f. (-25 C)
-Desired idle speed is 650-875 RPM.
-ECT is greater than 140 deg. F (60C)
-No ECT, EGR pintle, MAP, misfire, vehicle speed or TP sensor DTCs are set.
Notice the last one makes refernence to the misfire DTCs that you just solved :D
Looks like we need to check the IAC terminal resistance next.
Sunday, March 11th, 2007 AT 8:07 PM