So I’ve been chasing down an idle issue for a month or so now after I got my rebuilt 1.6L back in the Miata with a turbo on it. I’ve patched several vacuum leaks and have done various tests for other leaks and I’m positive it cannot be a vacuum leak anymore. My iacv seems to work just fine it opens, closes and I can hear it moving around in there. I have my idle loop set to pmw open loop and I’ve been messing with the table trying to get it down but I still can’t get it down past 3k rpms. I’ve messed with the idle screw and the rpm idle targets. I’m running an aftermarket intake manifold so I have all the coolant lines for iac capped off. Can someone guide me what settings I need to mess with for the idle to come down or the right settings for deleting the IAC entirely? I’m not running AC so I have no issue deleting or plugging the valve.

 

As always, posting a tune and log is the first thing you should be doing.

Is this a SpeedyEFI unit? What kind of values have you been trying in the IACV PWM table? I'd start at 0 and increment in steps of 10 and see if you get a change anywhere.

My hunch is that you'll start to see movement around 90 duty cycle.

 

What's your iacv's operation direction? mine has to be reverse, if I set it to normal it idles very high, somewhere around 3k