Spontaneous Idle Hang
 

Drive the car earlier in the day; everything is fine, just as it has been for a loooooong time. Park, come about two hours later, and the idle shoots up, hangs, and starts bumping off overrun. The only other time I've had this happen outside of learning2tune is when I was fooling around with engine state PID activation. Prior to this happening, the only thing I changed in TunerStudio is the EBC frequency while reading up on here about tuning it. I've checked the obvious suspects: Vac leaks, rechecked my advance offset (hasn't been touched in a while), tested injectors, spark outputs, and IAC valve. Everything is good. Usual idle MAP is in the 26-28 range and was fantastic before this. I have the feeling I'm missing something obvious, but can't find anything that I can link to the sudden problem. Tune and long attached. Note that I turned off overrun fuel cut while trying to diagnose the problem, and adjust the idle VE table because it was running lean (due to the MAP being off the table).

Update: Reflashed the firmware (using 1.5.2RC12) and it looks to have solved the problem. Never had this happen before over the last 14 months of using MegaSquirt, but there you go.

Yeah, this didn't work. Started fine, warmed up, and got down to the correct idle speed as normal, and as soon as I touch the throttle it hung at about 1150 RPM. Changing the trigger offset in the ignition settings allows it to rev and return to idle normally, but the timing mark on the damper is nowhere near the marks on the timing cover. Damper looks fine, with no cracking or other damage. Stumped.

I think you need to go to engine state settings and lower your overrun MAP threshold to something like ~21 kpa.

When you tap the throttle in your log at 84 seconds you exit closed loop idle and MAP drops below 25. Since with your settings anything less than 25 kpa is suppose to engage overrun it never drops back to closed loop idle.

I'm not sure what the reasoning was for changing your trigger offset but I believe the reason it returns to idle is because the timing being off has decreased VE which increases MAP enough to keep you over 25 kpa. Change the trigger offset back to what it should be and adjust your overrun settings. If you still have issues get a fresh log with those changes.

Changing the trigger offset allowed the RPM to drop back down to idle range. With the offset at the correct setting (ie, the timing mark on the crank pulley aligned with the cover mark) RPM would hang at around 1150.

Going to try your suggestions here in a few and I'll report back. Thanks.