AFRs Not Reading At Idle
 

So with the megasquirt installed and working, at idle, my innovate MTX-L displays 22.4 on the gauge. If I give it gas, it'll jump down to 14-16 briefly and quickly go back to 22.4. I've read that an exhaust leak can be the explanation. Thing is, the AFR acts completely normal when the stock ECU is installed... so it has to be the tune, right?

But what about the tune could be causing this? I've tried adjusting the timing all over the place. Anywhere from 10°BTDC to 18°BTDC at idle. It likes 16 or 17. But I can't get the fuel load right without an AFR. Ideas?

Assuming this is a serious question (and if you are serious, then so is your situation).

Read the Megamanual: proper one for the MS you have:
Megasquirt Manual Index - Megasquirt EFI

Set up fueling according to injector size, etc. Then tune the VE table.

22.4 usually indicates fuel cut off or error. I don't know how it can be idling higher than 16~18ish.

22.4 = normal outside air... Did you calibrate it properly?

The fueling is set up properly. I'm running the base map for my 1.6, so the VE table should be at least in the ballpark.

Yes, I've calibrated it twice. It works fine with the stock ECU in place, though... it's probably idling really rich based off the smell.

Rich enough to misfire will read lean, as there will be free O2 sensed.

You say you're adjusting the timing. Three things.

1. Did you set your base timing with a timing light? And check the timing megasquirt is outputting is the same physically shown. Hint: Lock timing at 10, it's in the manual
2. Did you go into the fuel table and add fuel? Fuel Settings>Fuel VE Table 1 (high light around where your car is idling and hit the > key to add fuel it should richen up.
3.A base map is just that. Your car could definitely have another issue, but try adjusting the fuel mixture, not the timing map to adjust AFR. Timing should be floating around in the timing map and shouldn't really effect idle other than idle RPM, If you don't have a Idle air control valve. Once the fuel map is dialed in, Lower/raising timing lower/raises RPM as well as transitions your part throttle response.

Hey guys, it turns out the car was just dousing the sensor in fuel. Waay too much. And because the sensor read LEAN, the auto tune program only wanted to make it worse... I took it down a bunch until the sensor started working again. It's going well, now. Thanks for your help.

That's a tricky one to figure out for people who don't tune all the time. When you're adding fuel and the gauge is reading fully lean and non-responsive, definitely counter intuitive. But the strong smell of un-burned fuel is a easy way to establish the car is not running lean as the gauge is leading you to believe.

Make sure you change the spark plugs once you finish getting the idle and drivabilty close, they'll definitely be too fouled out for boost.