No fast idle on 90-93 MSI
 

Hello!

I've been tuning the hell out of my Megasquirt lately, and I've got the car to run smooth as hell. I'm a happy camper! But there's still one small niggle to be solved.

I searched on this matter here, and on other forums, to no avail. I can't figure out why my car isn't fast idling. I've double and triple-checked all the configurations and nothing seems wrong.

These past few days I've been hand tuning the VE Table, and some other things. However, due to some unforeseen factor (could be the cold weather, or something I messed up while tuning) the car now idles very rougly right after startup. I had this happen the first times I started the Megasquirt, but then it was pretty normal so I didn't pay much attention to it. Now it is back. When I turn the car on, the engine starts then the idle oscilates heavily, and almost (or sometimes even) stalls. I need to put my foot on the accelerator, to keep the revs at 1xxx rpm for one or two seconds, and it stabilizes, but when it does, it goes around 950 RPM which I reckon is the slow idle.

Also, it only does it when cold. While hot, it starts and idles just as it should! And when cold, the idle works fine, only it slow idles. The stumbling and stalling is only on startup.

My fast idle is set for 1400 RPM, and since this is a '91 Miata, it has no fast idle valve, just the regular ol' PWM idle valve. Could it be a problem with that bypass valve on the side of the inlet manifold? Still, this doesn't explain why it doesn't fast idle. It must be a tuning issue.

Anyone that can shed a light on this matter, will be greatly appreciated!


Idle settings:
https://www.miataturbo.net/attachmen...ine=1336348675

Exactly what ECU do you have? You said you had a DIYPNP, which is MS2 based, but the screen shot you posted is for an MS1.

It's one of Brain's DIYPNP MS1 units, not a recent DIYPNP ;)

so it's a MS1 cpu on a v3.0 board and a hand built PNP harness?

Yeah that's it! Standalone version.

I have been fiddling with the idle settings quite a bit, but I have gotten nowhere...

It just struck me that I must have something misconfigured, or my idle valve is bad. I fiddled around with the settings on a friend's NA who has a BP-ZE engine, and the changes in the settings resulted in the idle behaviour becoming much different. I see no changes in my car.

I also recall my car used to stall with the OEM ECU. It doesn't now, but it does have that erratic behaviour on engine start.

I'm currently back to the default settings that come with the MSPNP_90-93_NoAFM default tune. Is there any way I can test the idle valve?