Code E-21 is Mass air flow sensor signal circuit malfuntion
Code E-23 is Throttle position sensor signal Circuit Malfunction

Did both set at the same time? seems strange for these two,one thing i would check is the battery condition and make sure the Alt. belt is tight. Sometimes can get some strange codes if battery is getting bad or belt is loose,as for clearing the codes follow the instructions,tho the throttle code might not clear with the pedal dance,might have to unhook the battery cables for a bit to clear them.

"The Pedal Dance"
Turn the ignition switch on with accel. pedal released,after 3 seconds fully depress the accel pedal 5 times within 5 seconds(end in released position). After 7 seconds(timing is very important...1 mississippi 2 mississippi etc....) press and hold down accel pedal for approximately 10 seconds(again timing) until the hour meter starts blinking, release pedal and push down and hold again for 10 seconds) hour meter should be on with no codes showing,shut key off and test to see if codes cleared.