I have an S5 NA swapped GSL-SE that's running on the GSL-SE ECM, injectors, etc. and I can't get it to hold idle when the car is stopped and I put the car in gear with the clutch in. I can hold the clutch down with the car in neutral and it idles fine, but it drops as soon as I put the car in gear. With the swap including an S5 intake, it likes to idle around 1100rpm and I can't get it any lower than that. I pressurized the intake and found no vacuum leaks so I assume it's just due to the S5 intake flowing more.

I've gone through the whole GSL-SE idle adjustment procedure with my GSL-SE TPS and it's set correctly. I started troubleshooting as outlined in the service manual by testing the neutral switch on the transmission. It tested good. I also tried the BAC test by unplugging the vent and vacuum solenoids with the headlights on, but idle did not change. I read that that can be normal though when your idle is above 800rpm, so I am not sure if my BAC is working correctly or not.

Any ideas on what to test next? Other ways to confirm that my BAC is actually doing its job?

 

clutch switch? its a big problem on the FD/Miata's when its bad the ecu doesn't go into "idle" and rpm droops

 

I assumed if it were the clutch switch, the idle would drop when I push the clutch in and not just when I put it in gear? I'll check it regardless since it's simple. I also have an issue with the car occasionally not cranking so you maybe onto something

 

Fixed it!
It was the clutch switch. I thought it was OK because the plunger seemed to work. I finally put a multimeter on it and it had no continuity at any point. I took it apart and cleaned all the corroded contacts and it worked fine after that!

 

that's great to hear.