E85 idle issue

[valsperformance]

The engine is a 434 stroker at 13:1 w/ 248 252 @.05 solid roler w/720 lift. It runs on E85 as stated and the IAC counts are very low at 950 rpm (0-25ish). When I put the car in gear or stab the throttle at idle in park she dies. I can force the IAC open to around 90 and everything is great but the STIT's are then way off and it bugs me. It seems to want more air but the IAC's indicate otherwise. The A/F at idle is set to the highest vacuum. What gives here? If anyone would like to look at the tune I can post it tonight. It is not complete, just enough to start and move the vehicle.

[valsperformance]

OK, when I lean her out at idle and hold the timing very steady 24ish and let her chop a bit the idle is actually more stable w/ less vacuum. Is this inherent of alcohol?

[goatkart]

did you change your stoich a/f to reflect the new stoich for e85/alchol? i think (confirm this) it is 9.7:1...

[valsperformance]

First or second thing that I did.

[n0dih]

Make sure you have enough heat on the incoming air and warm fuel. Ethanol has so much lower vapor pressure (RVP) that cold temps, <35 cause the exact condition you describe. Not enough RVP to make combustion work well. You may need to richen it up to get more vapor available to make good cold drivability.

What does setting the stoich do with a NB O2? In my OBD1 LT1 I run E85 and change the fuel constant much lower and all fuel calculations fall perfectly in line. Does it do much the same with the fuel calcuations?

Do you have enough cold timing? Enough idle timing? Ballpark 29-30 degress over base timing for advance (warm engine). Again, ballpark... Especially when cold. I am able to set cold timing adder (I am sure you can as well) and adding an additional 5-8 degrees over warm timing keeps cold drivability good.

[valsperformance]

That is exactly what might be happening here. The intake temps were less than 35 degrees since I was tuning outside. Monday I will richen it up a bit open loop and extend the open loop to close loop transition even longer than I already have. I can base it on intake temps being over 50 or something and coolant temps above 140 or so. That should bypass the issue when cold. I will also try some additional timing when cold.

The O2's work fine and the tables seem so far, to be close. I assume the VE might ramp up a bit quicker but we'll see. It did require more startup fuel though. About 20%. I guess the A/F for start up must be like 4 to 1 or something crazy.. but it starts.

Thanks for the explanation. This must be why it idled good in the shop when I pulled her back in.

[valsperformance]

Tune and just a brief log at idle. I think I was messing with the IAC's in the log so prob not much help.