/diy/ - Do It Yourself

For the life of me, I can't get this stupid circuit to cooperate with me, when my motivation to build it was for the fact that it was simple. Thought maybe someone here could give me their input.
So what I'm trying to do is use a thermocouple to measure the temperature of an oven, and output it to my laptop via an 8051 dev board (that I made in school ages ago). The circuit I'm using to measure said temperature is this AD595, whose output I connect to a MCP3008 so that my 8051 can read the temperatures.
When I hook everything up and output the temperature to my laptop, I get readings that are 5-10 degrees higher than what the room temperature is. When I touch the thermocouple probe to warm it up, the temperature starts going down back to the actual room temperature. As soon as I let go of the thermocouple, the temperature immediately spikes up to something like 40C and slowly goes back down to being around 5-10 degrees above room temperature.
1) I know for a fact that the 8051 is not the problem. It works for every other application that I use it for, so I know that the circuit I'm plugging to it is the issue.
2) I isolated the AD595 from the MCP3008 and tried measuring the output with a multimeter. To my surprise, the voltage reading I was getting was exactly room temperature. I was able to rise the temperature by warming the probe with my finger. Clearly, the AD595 is not the problem.
3) I checked to make sure all the pins on the MCP3008 are connected to their respective pins on the 8051. No issues there.
4) I have tried switching the MCP3008 with 3 other fresh MCP3008 ICs. Still no dice. The MCP3008 is not the issue.
5) Just by accident, I left the negative probe of my multimeter connected to the ground of my circuit while running my program to read temperatures. This apparently solved the issue because the temperature readings were being spat out perfectly, and would change based on whether I'd touch the probe or not.