Went to Autozone and had the car scanned. Only two codes came up:
P1088 - tumble generator valve #1 (RH) position sensor circuit low output
P1086 - tumble generator valve #1 (LH) position sensor circuit low output
I guess the valve is no longer stuck. At this point, it seems like the best way to go is to replace both sensors with the throttle position sensor. If anyone has any other ideas / suggestions, please let me know.