AC idle up!

Grinds starting with Critical Start, Co-Pilot, Pro Services, consultants etc vs DIY hard knocks RTFM into production. I’ve done things both ways, with this MS3 stuff I’m going to lean on an expert and develop my foundational techniques as well.
 
Required said:
Grinds starting with Critical Start, Co-Pilot, Pro Services, consultants etc vs DIY hard knocks RTFM into production. I’ve done things both ways, with this MS3 stuff I’m going to lean on an expert and develop my foundational techniques as well.
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Nothing wrong with that. I tune my trucks 99% of the time but I know when to ask for help as well. Nothing wrong with getting a little help.

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Raymond_B said:
I do not know anyone who has tested the PWM Ford vs the GM stepper, although the guys that do use them have no problems with Megasquirts or other EFI and getting them dialed in. If I swap over to the Motion Raceworks TB I'd have to use a GM stepper. Anyway I think the moral of this story is exactly how Jamie phrased it, you're simply managing engine TQ at various loads (AC, fans, or in/out of gear, etc, etc are a sudden load) no different than any other area of tuning and the best tool at your disposal is timing. I will say this, you've 100% have to get your idle AF right before diving in to idle timing and control, all too often people want to do idle 1st, but for me that's later on as you get other things sorted.
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I'm going to think out loud for a minute. Going back to the original statement that the IAC just isn't fast enough, how fast does it need to be? It can open in a small fraction of a second. Likely a similar amount of time for a spark adjustment to take affect. How long it takes for the air to start moving into the engine is another matter, but it seems to do OK on a stock truck. So is the issue really the speed of the IAC? Or is it a loss of low end response of the engine due to a cam change or something else? As with everything it's a matter of the combination working together and using the tool that works best. If you can gain enough to make up for the AC load with timing, is your idle really optimized? Or should you always have that much timing in it? And if you did have that timing in all the time would the IAC work better?
 
oilwell1415 said:
I'm going to think out loud for a minute. Going back to the original statement that the IAC just isn't fast enough, how fast does it need to be? It can open in a small fraction of a second. Likely a similar amount of time for a spark adjustment to take affect. How long it takes for the air to start moving into the engine is another matter, but it seems to do OK on a stock truck. So is the issue really the speed of the IAC? Or is it a loss of low end response of the engine due to a cam change or something else? As with everything it's a matter of the combination working together and using the tool that works best. If you can gain enough to make up for the AC load with timing, is your idle really optimized? Or should you always have that much timing in it? And if you did have that timing in all the time would the IAC work better?
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Nothing will act faster than spark which is your first line of defense. You can make it work with just spark and I did, but the added help from iac does even better. Stock truck isn't as bad as you only have the compressor engaging with stock fan.. electric fans that pull a lot of voltage add even more stress to the system. Plus who doesn't like better cooling and charging at idle? I also know on gen 2 trucks that AC idle up is in stock strategy as I use it on my gen 2 as well.

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Stock truck still has power steering, AC and still goes in and out of gear (which applies/removes load). The only thing it doesn’t have is an electric fan.

Spark is WAY faster then the IAC, the IAC’s main job is to keep the idle at a specific rpm not to combat load being applied and removed.

Some vehicles don’t have an IAC and they only have spark as an option.
 
I use the IAC mostly for idle up at cold start. It will adapt for prolonged changes in load, like the AC being on, bur the timing always comes in first and then tapers out.
 
oilwell1415 said:
I'm going to think out loud for a minute. Going back to the original statement that the IAC just isn't fast enough, how fast does it need to be? It can open in a small fraction of a second. Likely a similar amount of time for a spark adjustment to take affect. How long it takes for the air to start moving into the engine is another matter, but it seems to do OK on a stock truck. So is the issue really the speed of the IAC? Or is it a loss of low end response of the engine due to a cam change or something else? As with everything it's a matter of the combination working together and using the tool that works best. If you can gain enough to make up for the AC load with timing, is your idle really optimized? Or should you always have that much timing in it? And if you did have that timing in all the time would the IAC work better?
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It’s a good question. It’s probably more of a percentage game of each. Timing being the larger piece of the pie. Maybe look at how much power each gives to overcome the load. Like the combo should be equalized to give some room on each one to scale out if needed. It works vs. it works and is optimized etc.
 
Required said:
It’s a good question. It’s probably more of a percentage game of each. Timing being the larger piece of the pie. Maybe look at how much power each gives to overcome the load. Like the combo should be equalized to give some room on each one to scale out if needed. It works vs. it works and is optimized etc.
Click to expand...
Agreed. This topic gave me flashbacks to the dark ages of carburetors and mechanical advance. Everybody set their timing to give max power with no regard for part throttle driveability. They'd chase idle and transition problems forever with car tuning when what they really needed to do was add 4-6 degrees of initial timing and limit the advance by an equal amount.
 
The thing I’m enjoying the most is the capability to fix all those little driveabilty issues like you mentioned. I used to just drive the car different if it didn’t like to cruise at 2600, I’d just not cruise at that RPM! Doesn’t like hot starts? Wait until it cools down lol
 
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