Carpokes

If helpful, I notice the MoTec chart is in microseconds. Divide by 1000 to get milliseconds, if that's what the MaxxECU software is expecting... I've screwed up many an Arduino program mixing those two up.

Thanks everyone. Will study up to keep fine tuning. Car does feel good though. I’m avoiding going into boost for now, but can’t wait to start playing with the electronic boost controller.

Dumb question, should I be shooting to improve my idle AFR to get closer to 14.7 or is mid 12 or so acceptable? This would be for an engine at full operating temp running in outdoor temperatures in high 80 degrees F. My idle is solid at about 850 RPM running open loop idle for now.

12 is way too low, mine seems happiest at 14.3

Bergerac wrote: Tue Jul 08, 2025 5:56 am 12 is way too low, mine seems happiest at 14.3

Ok, pretty much what I thought. Will keep working on improving it.

My car (89 S2) seems to idle best in the mid to high 12s, fully warm.

It doesnt like idling anything leaner than 13 or so (starts surging). Based on what I have read, batch fire cars tend to idle richer and that seems to be the case in real world testing on my own car. Switching to sequential injection should allow you to idle leaner.

I am also running speed density, so no air metering

Here is a good read regarding idle tuning - the principals should apply to any standalone system
https://www.diyautotune.com/support/tec ... egasquirt/

That’s what is throwing me off, the idle feels very good. Of course, I don’t know what theoretical “perfect idle” feels like. But it’s solid at 850rpm and it “sounds” right. If I adjust VE table, it starts to hunt a bit. So I don’t know, maybe my car is like yours and is happy in the 12’s. Though not sure what 16v vs 8v does to AFR. I’ll keep adjusting and see what happens but I’m not to worried about it for now.

For what it’s worth, I did have a wideband installed prior to installing the MaxxECU. My idle AFR was 14.7 with A-tune.

To be fair, 12s seemed pretty rich to me as well, but the car disagrees anytime I try to go leaner. Assuming my wideband is accurate at least (I just free-air calibrated it again this spring, which you should do every year).

In terms of timing, my research says to run the timing that gives you the most vacuum (lowest KPA) at idle. I am at around 15 degrees advance on my tune

I've been running 10deg which is the same as the stock DME, MAP is pretty much spot on 30kpa. I'm surprised you managed to get a stable idle at 15.

I have no metric for good idle apart from the sound and the feel of the engine,

Mine stank of fuel when it was running that rich to the point it would make me feel sick sitting in it to long.

Bergerac wrote: Tue Jul 08, 2025 2:20 pm I've been running 10deg which is the same as the stock DME, MAP is pretty much spot on 30kpa. I'm surprised you managed to get a stable idle at 15.

I have no metric for good idle apart from the sound and the feel of the engine,

Mine stank of fuel when it was running that rich to the point it would make me feel sick sitting in it to long.

I actually looked out for fuel smells/fumes but nothing out of the ordinary, even in my garage.

The thought of miscalibrated sensor has crossed my mind. Will try to rule that out, once I learn how haha

Stock camshaft? Some cams aren't happy at 14.7. I get a stronger idle in the 12's and 13's too -- using the DME on my 3 liter -- but keep it at 14.7 for smog. That sounds like a lot of timing advance for idle....