I think it makes sense to pick a middle number (0.7) to start tuning from, the goal when tuning timing would be to quiet the knock sensor so changes to IAM are miniscule. Its an arbitrary starting point really but starting from 0.7 would be good if you base your tune on say 92 and you occasional use 93 or 91.

Ok so on my car A01J ROM it has been hovering around 0.4 for a few days now even after sitting overnight. Could it be that it only resets if it is sitting above 0.7? Meaning if your averaging below 0.7 then it stays put over multiple cycles.

Why my multiplier is at 0.4 is another issue. No full throttle knock but massive tip in knock. Can hear it clearly, not just logged.

That is interesting. That's another test I'll have to try -- need to get IAM down below .7 to test though.

Not sure if you have a tune or not, but running on the stock tune has some awful tip-in knock. Tip-in enrichment needs to be increased.

-- Bob

Tune is stock at this point. Only defined rom for the A01J is from BRZedit, EPIFAN is awesome (thanks!). I can not only log the tip in knock but also hear it!!! So the theory that the A01 maps have resolved the tip in knock problem is busted. What I'll try next is to rest to 0.7 and then have it go towards 1 and then see if it cycles back to 0.7 after sitting.

The A01 ROM addressed the high rpm shift knock that was damaging the DI seals. A01 made no changes to tip-in enrichment. You need a tune to correct it. And yeah, I've been able to induce tip-in knock at will on stock FRS/BRZs, and can definitely hear it.

-- Bob

Observations on this having tunes from several tuners out there, and paying attention to the IAM. It seems that the ECU really wants to default back to the inital value, unless knock brought it down - The first tune I had had the IAM default set to 1 - and it always "stuck" at whatever it was between running it, hot or cold. It would reset if I reflashed, as I would expect. The second tuner I had I saw tunes that defaulted to 1, and .7. The tune that was at 1, would behave as the first tuner's did. The second, defaulted to .7 behaved differently. It would reset, as long as it was above .7 when it shut it off before. If for some reason it was below .7 on shut off, that value would stick around for the next crank over.

This seems to make sense - conservative as needed on start up, with room for improvement if all is happy.

Just my .02, but I don't think anything it does is out of character. I would also say that tuners should probably stick to tuning to .7, rather than 1. Let the ECU do it's job for the last little bit of power - less explosions and fireballs that way :)

I can't seem to find reference to how IAM scales the actual ignition timing. i.e.- how many degrees is an IAM change of 0.1 worth?

It's a global ratio. The base spark tables + spark advance table is where the lookup happens and then the various modifiers do their bit, including iam.

It is an Ignition Advance Multiplier that number is multipled against your ignition advance table and that value is then added to your base ignition table to get the actual ignition timing that the ECU utilizes. So if a table in the ignition advance table had a value of 20 and your IAM is 1 then you get all 20 degrees but if it is .5 you only get 10 degrees. Tuners can get around the IAM by zeroing out the igntion advance table and just increasing the base ignition tables.

Heh... Well... @mad_sb I have a new flash file from a new tuner that i flashed this morning. Iam value stuck around at 1 the entire time never moved. Not even on a restart.

Some tuners set the initial IAM to 1 to tune. Me included...;) If it's set at 1, it always resets to 1 on an ECU reset. What will be interesting to see is if your IAM drops below 1, will it stay at the lower level upon restart with the default set at 1?

I suspect what brn12345 said may hold true and explain what we've seen on both the BRZ and FRS.