Wemos D1 / ESP8266 Analog read problems!

I did a Temperatur sensor setup with a Wemos D1 but got alternating temerature readings.

I soon discovered it was the ADC reading different values even with fixed voltage at the analog pin. It has a range of around 10 (of 1024) where it dififfers.

Now I thought the board must be messy and took an ESP-12F but that's even worse, that has a range of around 50 where it differs!

The huge differencies are seldom and look like the Chip is doing something at an interval which interferes with the ADC.

BTW. not using WiFi for now in my sketch....

void setup()
{
  Serial.begin(115200);
}

void loop()
{
  Serial.println(analogRead(0));
  delay(100);
}

Any Idea?
If you're using the Wemos or ESP for reading analog values, what about your readings?

http://forum.wemos.cc/