With my big cams and lack of vacuum, I simply can not get enough air into my engine at idle when the AC is on during the hottest of days. I've read some people using a FPR solenoid wired in parallel with the AC, but I'm concerned about not flowing enough air. I know it's an airflow issue, as I can make the car idle at target RPM if I pedal it. Could anyone recccomend an on-off idle valve that I could plug and wire in with no drama? Or alternatively is there a larger PWM valve out there that I could just use to replace the stocker with?

TIA

 

Unplug a random vacuum line on the intake manifold while it's running. If that's enough, you can use any 12v solenoid found in every 90-05 miata. Such as VICs, VCTS, purge solenoids, FPR solenoids, etc. I've done this before with a 1/4" solenoid, I think off an MR2, so bigger than most of the 3/16" ones found on Miatas. It was able to high idle at ~1200rpm until the engine was warm, then I tuned the throttle bypass for a 900rpm idle on a welded Honda intake manifold which had no idle valve options.

 

Will try that next.

I just ASSumed that since I have to pedal it, such a small leak won't be enough.

Will report back

 

Your PWM max duty is probably too low.

 

Nah, I've tested it. Max is 70%. Going higher does not do anything. This car does not make much vacuum at idle, so it does not pull in near as much air as a stock car.

I popped a vacuum cap off the manifold this morning.. it 90% resolved the issue, but when the fan is on 4 and pulling some amps, it still needs just a bit more air. The idle is higher but not too bad. I'm thinking about drilling a small hole in the throttle body for just a bit more bypass, and then adding a solenoid. I can probably tune around the rest. I don't want to run two solenoids, so if that's still not enough air I'll look into something bigger.. a 1/4 inch one should more than do it.

 

So it worked fine in the morning with one additional vacuum leak, but it couldn’t handle the hot afternoon heat soaking in traffic.. I got it idling good, though.

for some reason, the MS sees the AC turning on, but it does not raise the idle DC as commanded in the AC settings, so I set it to add 600 RPM to closed loop idle when A/C comes on.. of course there isn’t enough flow in the IAC for that, but it did what I expected, raised the idleDC to my max setting when turning on the compressor. Still wasn’t enough air to idle at %70 DC, so I bumped the max DC to %80, which did the trick. It now idles with AC on, and the compressor drags it down to 1100-1200 RPM. My normal target is 1100. I also set the compressor to turn off at 800 RPM, so if the engine tries to stall, the compressor turns off. Default value is 300. Still needs the vacuum leak, so I’ll setup a couple old FPR solenoids in parallel. My ride home in traffic was downright frosty, no stalling.

without AC, the car idles perfect with 20-23DC.

anyone know why the MS won’t add the idleDC as requested? in A/C settings? I ASSumed again it was adding 20%, but tuner studio tells me it wasn’t.