Bigphily

Hi Guys,i have a 94 ls400 which used to start at 1900 rpm. i replaced the temp gauge, pulled the battery and ecu fuse and then put everything back together.i started the car and she started at 1100 rpm. i thought sweet problem fixed - WRONG. next day i started the car and it was back to 1900 rpm.what have i done wrong and how do i fix this issue.