LM35 Issues with incorrent values
Break your problem into three parts:


Check your +5 V DC voltage is correct and is stable.
Measure the DC volts output of the sensor and compare it with the expected value using the formula in the datasheets.
Use a potentiometer or pair of resistors to generate a voltage into your ADC and see if you get a correct and stable reading.


If (1) fails then you need to find out what's wrong with your power supply.
If (1) is OK and (2) fails then you have faulty sensors.
If (3) fails then you have a faulty Arduino or faulty code.



Report back.