BTW, 123 is a TPS code, and it should be corrected before you go any farther. Code 998 is not good, but you have to eliminate the TPS code first. Don't forget to reset the ECM after correcting the TPS code, then run KOEO codes again. If you get a 111, then run the KOER codes, and see if 998 is still there. Post the results.
Take care,
-Chris