LM35 to Arduino malfunctioning after connecting GSM

Hi,
I am building a temperature monitoring system using lm35, GSM Sim900a and Arduino.
LM35 was working good when connected with Arduino and readings were as expected. (without connecting GSM)
But as I connected GSM Module to the same circuit, Temperature readings started fluctuating in a wide range (24>>38>>31>>50>>etc.)
I am using USB Power for Arduino,separate 12v adapter for GSM and simple male to female connecting wires for other connections.
Please help me with the solution.
thanks.