High Idle PWM% Reading
 

I seem to have my idle tuned in ok, but one thing i haven't managed to get right is coming back to idle when coming to a stop.

When i come to a stop the revs drop very low down (400-500rpm). Today, the only way i found to stop this is with a PID Duty percentage of around 35%.

I also noticed, while at idle the Idle PWM% gauge reads around 36-40, and also the CL idle indicator seems to be highlighted red. Is this correct, or should i have a lower value than that at idle?

Please post a screen shot or your .msq.

Review this thread. https://www.miataturbo.net/megasquirt-18/timing-idle-requesting-some-help-57133/

It appears he has MS2. That thread will only be so helpful.

increase the dashpot.

Tonight i increased the dashpot from 3 gradually up to 10 and it didn't seem to have any effect on the drop in revs.

I've attached my .msq If anyone would take a look at it and give me an opinion on whats wrong, it would be appreciated.

Mike

Change the valve closed duty back to 19.9 and then open the manual bleed valve on the TB.

You want the car to maintain it's idle when as heatsoaked as possible with maybe 1% DC from the Idle valve.

Once the car's 'base' idle is set the idle valve won't have to work as hard to maintain your target idle speed.

Surely opening the bleed valve would raise the idle though? At the moment it will idle at a steady 860rpm, which im happy with. it only drops below this when coming to a stop which is what im trying to solve.

With the closed duty set to 19.9 while driving the idle gauge reads around 21.9 but then goes back up to around 37 when it comes to idle. Should it be at the lower than the 37% at idle?

Mike

yes, but you're holding 860 rpm because the idle valve is doing 35%DC when the car is hot, so when you unplug the valve the revs drop considerably.

The valve is having to do too much, so close the bleed valve a bit, the valve will close more to compensate, your idle will stay the same but you won't get the idle 'dip' as the valve doesn't have to suddenly ramp up to pull the idle higher.

Ok, il give that a try tomorrow.

So i need to open or close the bleed valve? as you mentioned opening it in your previous post. I dont think will will close much more, i think it may be near the end of its travel.

Sorry open, was late. Unplug the IAC when the car is really hot, you should get barely any drop in idle speed.

I opened the bleed screw and it seems to have solved the idle dip problem.

However, when i unplug the idle valve instead of the idle dropping it rises to around 1500rpm. I guess this isn't normal?

Also since it was unplugged (and plugged back in) the idle pwm% gauge is now in red, it still reads the % just the whole gauge is red.

thats normal, failsafe mode.

^ see? I dunno how to set the idle screw in failsafe mode. Perhaps the air passage should be capped as well as the valve being unplugged, to set the bleed screw?

im pretty sure that's why you'd jump GND and TEN to set the idle speed it locks the timing as well as holding the valve shut.

easy enough is just close the idle valve with your ECU, then tune bleed valve.

^ D'oh! I forgot about that! How do you do that with Megasquirt? Shut off the valve completely I mean...idle control off?

You could use the idle valve test mode, set the duty cycle really low

AH! Thanks!

Eh? I don't get it if I pull the plug on my IAC valve my revs drop. I've never heard of/experienced this failsafe mode, and I've tried it on met year MX5's...

That means that your idle air is being provided by a combination of the idle valve and the throttle bypass screw setting. If you have it so that the throttle bypass is providing all your idle air, and only use the idle valve to add air for increased load or warmup conditions then if the valve fails you'll still idle properly once warmed up and without a ton of extra load

?? No it doesn't. Other peeps are saying by pulling the plug on the IAC revs rise, that implies that the valve is fully open when off which is in direct contradiction to every expensive I've had on a 5. I.e. Everytime you pull the plug on the valve, it closes/turns off/revs drop.

This is on both aftermarket ECUs and stock FWIW

What yourdescribing Pete is the correct operation of the idle valve I.e. It adds supplementary air when required to maintain the idle target.