Hi @jrl290
The analog inputs are not buffered on the Spark core, so 3.3V divided 2 or about 1.7 V is correct when the inputs are not connected. This is how the analog inputs work on the ST Micro ARM processor.
You need to drive the analog input with a medium-to-low impedance source (under say 20k ohm) to get a good value.
Have you tried adding the capacitor to the TMP36? That is known to help with that particular sensor.
Another thing to try if you think it is not working is a two resistor voltage divider with resistors 10k ohm or less tied to 3.3V* and GND.