Idle Fluctuating
 

Hello Everyone,

I am having trouble setting my idle on my 2001 VVT swap in a 95 Miata with Megasquirt 3 Pro.
It is jumping from 1400 rpm to 800 rpm to 1400 rpm.

At the moment, everything is stock besides the ECU and MSPNP DIYPNP IAT temperature sensor kit - Aluminum Bung. I do not have the VVT set on but it is wired up.
Any thoughts? I've attached the datalog I recorded.

It's popping in and out of idle mode. Either you have a leak in your intake manifold, your throttle cable is too tight, your idle bypass is open too much, or your idle settings aren't correct. Can't do much without a tune, but judging from the idle valve being at 2.7%, I'd say you have a leak, but again thats a stab in the dark without a tune.

Thank you for your reply. I'll check for any vacuum leaks. I am planning on getting a tune but I was really confused about what was going on. It did fluctuate from Idle to overrun.

A not-quite-tight-enough alternator belt has introduced this same thing in my car at one point too

Hello Everyone,
Well, I did check out to see if I have a vacuum leak and there was none. I did double-check the alternator belt and tightened it but that did not work also. I did do a cold start and it was in the "Overrun" setting before it started to fluctuate between "Overrun" and "idling".
Any thoughts on this? I've attached the datalog again.

Is there a reason you’re not attaching the tune too?

Without seeing the tune it is hard to say. Make sure your ENGINE STATES settings are correct. If your throttle position sensor isn't calibrated properly or the idle setting for it isn't right then you could be having an issue there.

For example if you're at 3% throttle with your foot off the gas at idle but the engine state is set to 1% then the computer doesn't know that you're within a throttle range to idle the vehicle.