This one has me stumped.

Car is a 1999 running Adaptronic, which is MAP based. Begi S4 kit.

Driving home Saturday night the idle increased from ~1,200 to 1,800. I figured it was a setting in Adaptronic I needed to adjust.

No setting in the software will pull the idle back down to something reasonable. I unplugged the IAC and turned the idle screw in to its stop to no effect.

Since the ecu is MAP based, leaks in the intake plumbing shouldn't matter, only those post throttle body should. I've checking high and low for leaks and haven't found anything.

Is there something I'm overlooking; a common problem like a faulty EGR or IAC valve perhaps? If you can point me in the right direction I owe you an E-beer.

Thanks

 

I just had a similar issue on my Hydra, was idling at 2,000 and wasn't cutting fuel at decel. Checked the throttle physically, and there were no issues and there were no vacuum leaks. Thought it may be loss of IAT signal as that caused this issue on another local turbo Miata, but that was not the case either.

Turns out the numerical setting (which has been working fine for a while now?) for the closed throttle position was too low and the Hydra thought the throttle was at "1" instead of "0" and was not entering closed loop fuel control. IDK if the Adaptronic is the same way, but it's something to check. Anyway, adjusted the setting per the manual to ensure the TPS reports "0" at closed throttle and all was well again.

 

either your throttle plate isn't shutting or there's a leak somewhere in the manifold or fuel injectors.

 

hmm. Can the IAC get stuck partially open?

 

Are you running open loop or closed loop right now?

If open loop, it could be your idle air values or Base Idle Value (coolant temp). These are found in the IDLE tab. If you are getting the higher values while your laptop is hooked up, find the current water temp or IAT in the Gagues section and try manually dropping the corresponding values in either the air or water section to see if that makes a difference.

Won't hurt to try them and you can always return them to the original settings.

 

Idle valve can fail in any position. With stock computer, key to run but engine off, you can hear the idle valve hum. Don't know which computer is running your valve with your set up.

 

IAC was gummed up. It would open fully under cranking then settle to its preset value to maintain a 1,000 rpm idle. The next time it had to move, in this case when adding extra effort for power steering, it would get stuck. Cleaning and a light misting of WD40 did the trick.

Thanks guys.