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Discussion Starter #1
Been using the holley DBW for a little longer than a month and love it, but I have a problem with the idle surging after it starts, seems to be a little worse on cold start.

It cranks over about 3-4 revolutions, and fires up but surges a couple times before the idle stabilizes. Anyone have any ideas?

Ive noticed the IAC parked is measured in %; but 15% iac parked does not equal 15% actual throttle opening. Is the iac ramp down hold position the same way? Im about ready to just log the start ups and start changing things just to see what it will do, and to see how much 5% changes in the software correlate to throttle angle
 

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The "IAC" on the dbw throttle body is 0-100% "IAC position" for 10% of the throttle if that makes sense. Since there is no IAC, is uses the first 10% of the throttle to modulate idle.
 

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Here is the way it works, it can be a little confusing, but it's not really. I just make it sound that way.. Needless to say there is no "IAC motor". What we did was create a method where the user can use the same idle parameters for a cable throttle body, or a DBW. Actually ended up working out well.

On the TPS vs pedal, the left most value for the TPS is basically your "stop position", like a setscrew on a mechanical throttle body. You increase that value until the engine reaches target idle speed, same as you would with a mech TB.

The TPS % from 0-100% (fully seated to fully open) is the actual fuel mechanical travel from fully open to fully closed when you do a TPS autoset. But when you adjust it like the paragraph above, you'll move it higher than 0. So say it is 5% (again, same as adjusting a throttle plate on mech TB). So then the ECU considers 5-15% TPS your "IAC area" (0-10% TPS movement above this value). It is allowed to move the dbw valve from 5-15% in this case to adjust idle, which is used as 0-100% IAC travel. So using this example, if hte IAC is at "50%", the TPS would be at 5 + 10% (tps percentage) *.5 (50% IAC opening) = 10% TPS (resultant TPS).

So when you set the left value in the TPS vs Pedal, you want to increase that left value until the IAC setting is about 5-10% hot idle in neutral, same as you would with a mechanical throttle body moving the set screw.

Clear as mud?
 

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Ha ha, clear as mud! Doug, I have not looked at the DBW stuff, I know you have it on your engine (at least on the BBC). Can the max opening be controlled, IE: I only want someone to get 25% or so of full throttle?
 

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Yep, had been waiting for some index racing to come this way to try that. Had the twin DBW's on the BBC, but a single on the turbo LS now.
 

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Discussion Starter #11
Doug I had the basic understanding of it but didn't see anywhere in the instructions/help of how much the "IAC" to actual blade opening ratio was. Thanks for clearing that up.

So I assume the IAC ramp down hold is the same principal?
 

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Discussion Starter #12
Interesting. Can the HP do DBW or just the Dominator?
Only the dominator. I have a specific tune now I call "valet" that only allows the throttle to open 35%. Its to force my self to get good mileage and prevent speeding tickets for drag week. The temptation for WOT fun is hard to resist with turbos.:p
 

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Here is the way it works, it can be a little confusing, but it's not really. I just make it sound that way.. Needless to say there is no "IAC motor". What we did was create a method where the user can use the same idle parameters for a cable throttle body, or a DBW. Actually ended up working out well.

On the TPS vs pedal, the left most value for the TPS is basically your "stop position", like a setscrew on a mechanical throttle body. You increase that value until the engine reaches target idle speed, same as you would with a mech TB.

The TPS % from 0-100% (fully seated to fully open) is the actual fuel mechanical travel from fully open to fully closed when you do a TPS AutoSet. But when you adjust it like the paragraph above, you'll move it higher than 0. So say it is 5% (again, same as adjusting a throttle plate on mech TB). So then the ECU considers 5-15% TPS your "IAC area" (0-10% TPS movement above this value). It is allowed to move the DBW valve from 5-15% in this case to adjust idle, which is used as 0-100% IAC travel. So using this example, if the IAC is at "50%", the TPS would be at 5 + 10% (TPS percentage) *.5 (50% IAC opening) = 10% TPS (resultant TPS).

So when you set the left value in the TPS vs Pedal, you want to increase that left value until the IAC setting is about 5-10% hot idle in neutral, same as you would with a mechanical throttle body moving the set screw.

Clear as mud?
I love when you post good tech info.
Please continue to do so...it's appreciated.
 

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Doug I had the basic understanding of it but didn't see anywhere in the instructions/help of how much the "IAC" to actual blade opening ratio was. Thanks for clearing that up.

So I assume the IAC ramp down hold is the same principal?
Yes, all the principles are the same. The nice thing is all the values are pretty much the same for a cable tb or a dbw throttle body on the LSx throttle bodies.
 
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