P1150 DTC from Scangauge II

For several months I have had on/off issues with DTC P1121 on my 2004 coming on, which seems to be either a throttle position sensor or a coolant valve problem, but since I detect no coolant fill issue, I have continued to clear the code w/my Scangauge and sometimes it would stay cleared for a week or more. For the last week, it only stays clear for a few miles. This morning I got a P1150 DTC, for which I can find no info, so I am reluctant to drive it much without knowing the meaning/source of this code. Any advice for a DIYer who really doesn't like Autoway Toyota's service department.