Sip/Puff Level is sticking at a low level
Please check, if the pressure sensor (8 pins, with a tube plug) is soldered correctly.
Sip/Puff Level is not at 512 +/- 5 if idle
In most cases, this is caused by pressure sensor which is not working with 3.3V. Freescale is sure, that it works (they canceled the dedicated 3.3V series). However, sometimes it doesn't. If the level is either very low or very high, but responds to sip/puff actions, please adjust the sip/puff levels to your needs. The default values are set for sensors with an idle value of 512.