The origin of hot air is no longer a mystery. Much to the dismay of many respected physicists, you have scientifically proven that hot air does indeed NOT rise, it falls below in worthless postings on websites. Thank you. Future generations of science majors will now need to pay exhorbitant fees for newly written textbooks.

Hopefully any other posts will be not be a complete waste of my time.

I am wondering if there may be a vacuum control issue. The vacuum lines are very brittle with age. Could a vacuum leak elsewhere in the system cause the expansion valve to not perform correctly while not causing the engine to run in an obviously irregular manner?