Cheng was made a commanding general of the imperial guards, but was not satisfied, as he wanted to take over Li Fuguo's power, and therefore he secretly plotted with Emperor Daizong.
The general Li Huairang (李懷讓), the military governor of Tonghua Circuit (同華, headquartered in modern Weinan, Shaanxi), was also falsely accused by Cheng and committed suicide in fear in 763.
Throughout the spring and summer of 763, Tibetan, or Tubo, forces were progressively attacking and capturing Tang prefectures to the west of Chang'an.
When Emperor Daizong issued an edict to the various circuits ordering emergency aid, however, the generals refused to respond, and Guo could not quickly gather troops large enough to resist Tibetan forces.
Emperor Daizong was forced to abandon Chang'an and flee to Shan Prefecture (陝州, in modern Sanmenxia, Henan).
The imperial scholar Liu Kang (柳伉) submitted a harshly worded petition, asking that Cheng be executed.
Putting on women's clothing in disguise, he secretly entered Chang'an and plotted to return to power.
[1] He was arrested by the Jingzhao Municipality government, and the imperial censors subsequently submitted an indictment against him.