I updated Nexus 4 to Android L, but many functions are broken. E.g, WeChat voice recording is broken, power ON button sometimes is not responsive. I am thinking to revert it to previous version. How to do that? thanks.
There's no "revert". The L ROM replaced the original ROM. If you want 4.4 or some other ROM, you'll have to find a flashable file and whatever tool you use to flash ROMs to the Nexus 4 (which I believe is an LG). Check the N4 forums on XDA.