BMW Repair: 95 525i wont idle, purge valve, position error

Question
Hi Got an engine that wont idle. No codes. runs fine off idle. Vac gauge reads very low at 1000 rpm 12hg. over 2000 rpm I have 28hg. I'm thinking a vac leak at the manifold.  The owner had replaced his gas tank due to a dent that he thinks was caused by engine vac. So the gas cap is missing, would this cause a start stall condition. The information display reads transmission program with key in second position. codes for trans are pin 6 not connected ignore error, and 105 MUX throttle position error. also noticed the ECU mite need programmed for cold start updates I don't think the ECU up dates are causing the start stall.
Thanks  

Answer
Joe, Intake manifold leak or related hoses are very common and is very possible. Missing gas cap should cause a check engine light. Check the purge valve for hanging open. This would cause a vacuum in the gas tank. As for the trans and throttle faults I don't know much about older DME faults.
-Evan