econjack:
What's the download URL for your LCD library. I've not seen one that asks for the clock and data lines with the begin() method.
I was having a problem getting the LCD to display anything via IIC, so I went through several different libraries. Turns out, grounding GPIO0 to get into programming mode prevents the IIC connection from functioning until the ground is removed. The library that I ended with was downloaded from GitHub - ahmeaqas/ESP8266-I2C-LCD1602: Library to control LCD1602 Liquid Crystal Displays like from ESP8266 mcu's through I2C bus and is working perfectly for me.