[NA] High Idle - IAC?
 

Hey all,

I'm in the process of getting the car up and running with MegaSquirt diypnp. However, as the title suggests, I can't manage to bring the idle down to a more normal level.
Immediately after turning the car on, the rpm rises quickly to ~2400-2800 and stays there (no fluctuation). I've setup everything I can including 10 degree fixed timing, map, iat, wideband controller; as well as double checking that the loaded base map is correct for the car.

I am suspicious of the iac being open, and that my ecu is not correctly, if at all sending correct pwm to the valve. Disconnecting the iac causes the car to stall out/not start. Blocking the iac bypass valve partially with my thumb allows me to bring the rpm down to a normal smooth idle. There appears to be no obvious vacuum leaks anywhere.

I am at a loss as to where to go from here, any advice on where to start diagnosing the problem further would be greatly appreciated.
Also if I'm missing any information please tell me, I'll provide anything.

Cheers,


1992 1.6 Mazda Miata. Stock with intake and exhaust mods.

what's the PWM IDLE DUTY % when idling/cranking?

you should be in low 30% to maintain ~900RPM

Inverted, normal, different frequencies, high duty and low duty % - nothing I change seems to have any effect on the rpm of its idle.

https://cimg6.ibsrv.net/gimg/www.mia...f50ebacba3.png

those idle settings are nothing like what a 90-93 should be using.

try the attached map.


but if thats causing high idle, you probably have a vacuum leak in the IM.

Thanks again for the help Brain, because those settings haven't changed anything I'll try to track down a vacuum leak.
Would it be worth reverting to stock ecu to see if the idle persists? I'm worried I didn't build the unit properly and consequently the ecu isn't controlling it.

I would check for vacuum leaks first. Mine had very similar conditions when i replaced a throttle body and did not get all of the old gasket off. Once I fixed that vacuum leak, everything worked perfectly.

I've hunted around for leaks, but in the meantime I also put the stock ecu back in. It's idling at about 850 with 10-12 degree timing and no change to the idle screw.
I don't doubt the functionality and performance of Megasquirt, but perhaps as mine was a diy kit, some component that controls the pwm on the unit has failed or I didn't install properly.

Are there any components in particular on the diypnp that might be worth checking or replacing at this point? Maybe reflashing the firmware and starting with Brain's .msq revision?

Thanks for your assistance :)