I have a 2001 Mercury Sable (24V DOHC V6) that has been having problems with its vacuum system. I live in Florida where the average temperature lately has been in the 80s.
I've been experiencing a very rough idle for roughly a month now that occasionally would stall the car. The car would start right back up with no issues and keeping my foot on the gas would stop the rough idle (Minimum ~1500 rpm).
I have since replaced the main PCV Valve elbow hose (not the valve itself, that's my next step) because it was collapsed. After doing that, my rough idle was almost gone outside of a jumping idle speed (between 600-1200 rpm) that would occasionally stall the car (easily started back up).
After that, I replaced my Idle Air Control valve which stopped the rough idle (save the occasional putt putt) but now my car would constantly run at a high idle (1600 rpm) and occasionally rebound back to normal idles which would sometimes cause the car to stall.
A few days ago the problems reached an all time high when my car dumped out all of its transmission fluid. I refilled the fluid (No leaks in two days???) and have since then only had the higher than normal rpm. I'm planning on replacing my transmission filter and gasket tonight since I suspect that is where the leak came from and I need it anyways per normal maintenance.
Does anyone have any ideas for me to try and fix next? My current plan is to do my transmission service and then swap out the actual PCV valve. I also have an issue where my vacuum operated AC switch (Controls which vents the air blows from) won't work and so my A/C will only blow from the defroster grid. This has been going on for years however and I don't think it is related.
I tried to be descriptive, please let me know if I've forgotten anything.