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Old 04-28-2009, 08:26 AM   #1
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Default High RPM after starting

Could use some guidance. When I start the car, the RPM hovers around 1500 and AFR is lean (14.5 - 15.0), all for the first few seconds. Then both the RPM and the AFR slowly settle down to reasonable levels.

So here's my primary question: what is the relationship between AFR and RPM during the startup/ASE period? I more-or-less understand the fueling side but I don't understand why it makes the idle RPM go high.

On a related note, I'm still having IAT heatsoaking issues, which are also accompanied by too-high RPM, even though my IAT sensor is way down by the IC outlet pipe (and therefore I shouldn't need a correction table.)

Paul's theory is that my IAC is the issue. But I replaced that not too long ago with a known-good unit.

.MSQ is attached.
Attached Files
File Type: msq evan_hr_49.msq (35.3 KB, 120 views)
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Old 04-30-2009, 12:11 PM   #2
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Hmm... your cold idle rpm is 1400, so when you start your car cold, it will hover there until it warms and will linearly fall to 900 RPM warm idle.

Also, there's a factor in the idle control (can't remember the name), that is basically a delay right after cranking where your idleDC is constant before closed loop idle takes over. This can cause higher idle RPM after crank, even if car is warm. I think default is 2.5 sec. You can reduce this, if you like. You might also want to try playing with your CrankDC factor to get a lower RPM after your car fires up. You might have to redo your crank pw if you mess with this, though.

If you feel your 1500 RPM fast idle is too lean while cold, bump up your ASE percentages at that given CLT.

Heatsoak issues with poor idle are a PITA... I use EGO to compensate for it. Is yours turned on (can't check msq right now, at work)? You might also want to check that your IAT is calibrated properly. On a cool day, when your car is at ambient temp (like parked overnight), make sure your IAT and CLT values are the same when you key on but don't crank the motor. Then do it again on a warm day. They should be close.

Try datalogging a crank/startup event and upload that.
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Old 04-30-2009, 12:16 PM   #3
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warmup enrichment
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Old 04-30-2009, 08:08 PM   #4
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Originally Posted by zzyx7 View Post
Hmm... your cold idle rpm is 1400, so when you start your car cold, it will hover there until it warms and will linearly fall to 900 RPM warm idle.

Also, there's a factor in the idle control (can't remember the name), that is basically a delay right after cranking where your idleDC is constant before closed loop idle takes over. This can cause higher idle RPM after crank, even if car is warm. I think default is 2.5 sec. You can reduce this, if you like. You might also want to try playing with your CrankDC factor to get a lower RPM after your car fires up. You might have to redo your crank pw if you mess with this, though.

If you feel your 1500 RPM fast idle is too lean while cold, bump up your ASE percentages at that given CLT.

Heatsoak issues with poor idle are a PITA... I use EGO to compensate for it. Is yours turned on (can't check msq right now, at work)? You might also want to check that your IAT is calibrated properly. On a cool day, when your car is at ambient temp (like parked overnight), make sure your IAT and CLT values are the same when you key on but don't crank the motor. Then do it again on a warm day. They should be close.

Try datalogging a crank/startup event and upload that.
Thanks! Very helpful post. I didn't know about cold idle RPM settings, etc.
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Old 04-30-2009, 10:37 PM   #5
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In addition, there is also a Cranking(DC) setting for the idle valve, which is typically larger than the average stable duty cycle. This is done to give the engine a little extra air while cranking, and after it switches from cranking to running it ramps down to start seeking normal idle.

Then of course there's the fixed MAP option during the immediate ASE period.

A surprisingly large amount of stuff related to the first few seconds of operation...
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Old 04-30-2009, 10:53 PM   #6
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In addition, there is also a Cranking(DC) setting for the idle valve, which is typically larger than the average stable duty cycle. This is done to give the engine a little extra air while cranking, and after it switches from cranking to running it ramps down to start seeking normal idle.

Then of course there's the fixed MAP option during the immediate ASE period.

A surprisingly large amount of stuff related to the first few seconds of operation...
Interesting.

In the idle control menu, the top setting is on "B&G" and all the options are grayed out - I'm pretty sure Paul said that is on purpose because the stock ECU controls my car's idle. Or are they grayed out just because I'm inside at my PC and not connected to the car?

Right now my fixed MAP value is 70, which is around 47kpa in my VE table for the 1500 RPM (virtual) column. I'll try increasing the fixed MAP to richen up those first few seconds.
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Old 04-30-2009, 11:20 PM   #7
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In the idle control menu, the top setting is on "B&G" and all the options are grayed out - I'm pretty sure Paul said that is on purpose because the stock ECU controls my car's idle. Or are they grayed out just because I'm inside at my PC and not connected to the car?
They're greyed out because I'm a retard and I forgot you were parallel.

Seriously though, When set to "B&G On-Off" it assumed you have a simple on-off idle valve, and so all the PWM stuff is turned off. Which is fine since you're not using it.
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Old 04-30-2009, 11:27 PM   #8
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it assumed you have a simple on-off idle valve
Do I? Or is the stock NB IAC more complex than that? (Put another way, are there alternative settings that might work better than what I've got currently? Paul supports the "less is more" theory re: only have MS control what's absolutely necessary and leave the rest to stock, and I agree. But now I'm wondering if it's worthwhile to add some complexity if MS idle control > stock idle control.)

Just say "no" if that question doesn't make any sense.
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Old 04-30-2009, 11:50 PM   #9
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Do I? Or is the stock NB IAC more complex than that?
No, you don't. And yes, it is. But since you have a parallel install, your idle valve most likely is not connected to the Megasquirt at all, and thus the whole idle section of the MS is irrelevant.
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Old 05-01-2009, 12:12 AM   #10
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your idle valve most likely is not connected to the Megasquirt at all
But is there any option or any reason to connect it? (I know that's a long shot, just trying to learn stuff here.)
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Old 05-01-2009, 09:41 AM   #11
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But is there any option or any reason to connect it?
Nah. Controlling idle is something that the stock ECU is quite good at, and it sounds like yours is behaving pretty normally from what I've heard here.
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Old 05-01-2009, 10:18 AM   #12
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crank settings, then warm-up, then ASE...consecutively.
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