I recently got an s5 TII and it has a few problems. Gotta press gas pedal down to start it, idle is low, and when ever I turn the A/C on the car idle goes up to around 1k then as I turn it to full (the A/C) the car dies. I am thinking it may may the BAC valve for the A/C and idle issue (could be tps for idle as well) any tips?

 

Ground the check connector by the battery to see what the warm idle might be. Hopefully it's around 800RPM. Then the TPS and BAC are the first 2 places to start. Check that the TPS doesn't have any flat spots and check reading at full open throttle to be certain that's correct. Set TPS @ 1k ohms, then do final adjustment using the Mazda checker. They say use a light, but you can use 2 MM or move the lead from one side to the other, back and forth. Then check the BAC. Not only does it work electrically when adding 12 volts, but does the inner part seal correctly, or does it leak. If it leaks replace the BAC. Have seen some success with cleaning, but after a month or so back to square one.
Actually I just replaced the TPS on my STII with a brand new one earlier this year, I had purchased it 2/3 years ago from a forum member, so when mine went south, changing reading at idle, and also giving a less than wide open throttle reading. I've also replaced the BAC with a JSpec back in 2001, so far so good, but once again there is a brand new one sitting on the self. These items don't last forever.
Good Luck