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#4331641 - 02/17/17 04:09 AM
Why are IAC Valves Heated?
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Registered: 12/02/05
Posts: 1128
Loc: West Chester, PA
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Why are modern computer controlled IAC valves heated with coolant? From what I have read, it appears coolant is there to prevent freezing. However, many believe coolant warms the IAC and controls operation. I think that used to be true with older designs where IAC valves had bimetallic springs and slowly closed as coolant temperature increased. With a computer controlled IAC valve, coolant lines to/from IAC valve do not affect operation, right? Thanks.
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#4331654 - 02/17/17 05:16 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 12/31/16
Posts: 5660
Loc: Waco, TX
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Some engineer felt it was a good idea.
I absolutely GUARANTEE you that "feature" isn't added unless there was a good reason for it.
If you can save $0.75 per vehicles over a million vehicles, that's $750,000 saved.
So, during the course of extreme temperature testing, someone felt it helped drivability in some way - - or it wouldn't be set up that way.
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#4331657 - 02/17/17 05:27 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 10/01/05
Posts: 299
Loc: Newport News, VA
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Air pressure drop as motor runs drops the air temp and could lead to iced up throttle valve.
Edited by sdowney717 (02/17/17 05:28 AM)
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#4331695 - 02/17/17 06:53 AM
Re: Why are IAC Valves Heated?
[Re: sdowney717]
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Registered: 11/09/08
Posts: 11532
Loc: NH
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Air pressure drop as motor runs drops the air temp and could lead to iced up throttle valve. That would be my guess, although stabilizing air intake temp is probably a good thing (attempting to limit the variables that the ECU map has to work around).
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#4331717 - 02/17/17 07:28 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 09/18/12
Posts: 5273
Loc: DFW
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The IACV (that's what Honda called it) in my 1989 Accord had coolant piped through it. So, this is nothing new.
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#4331772 - 02/17/17 08:42 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 05/17/09
Posts: 11840
Loc: N.H, U.S.A.
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Prevent freezing. Nothing new, Carb bases were heated with exhaust or coolant. PCV can plumb near there too which has a lot of water vapour during warmup.
If you were around in the 60s and 70s with manual choke and throttle you would probably had a carb freeze up a few times in the winter. My AFB on my 65 buick would do this - esp when I was late to class. Yes I did the heated base block off and intake stove delete for more power. Silly Kid, me.
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#4331800 - 02/17/17 09:17 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 01/13/17
Posts: 128
Loc: Montreal (West Island), Ile Pe...
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IIRC it is to establish a reading where inrush air can warm or cool on a 5V sensor to a baseline that would work in all climates.
If Cold there is less Resistance than when Warm, and this balance has to be within a sensible range to work where the PCM is only interpreting a Voltage 0-5VDC, and that window may not work in extreme heat or extreme cold so this problem is solved with the coolant warming (or cooling) in a range that the sensor can read a mid range.
Very hard to explain I guess that is my attempt this is a while ago.
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#4331805 - 02/17/17 09:20 AM
Re: Why are IAC Valves Heated?
[Re: The_German]
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Registered: 08/20/03
Posts: 12485
Loc: NE,Ohio
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IIRC it is to establish a reading where inrush air can warm or cool on a 5V sensor to a baseline that would work in all climates.
If Cold there is less Resistance than when Warm, and this balance has to be within a sensible range to work where the PCM is only interpreting a Voltage 0-5VDC, and that window may not work in extreme heat or extreme cold so this problem is solved with the coolant warming (or cooling) in a range that the sensor can read a mid range.
Very hard to explain I guess that is my attempt this is a while ago.
Are you talking about a MAF sensor? they are talking about the IAC. Idle air control valve.
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#4331813 - 02/17/17 09:28 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 06/28/03
Posts: 5603
Loc: Illinois
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Almost all throttle bodies are heated by the coolant. First mod I do is to bypass the coolant hoses.
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#4331837 - 02/17/17 09:46 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 01/13/17
Posts: 128
Loc: Montreal (West Island), Ile Pe...
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Rand you are correct I didn't read it right.
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Independent Honda Sales, Parts and Service
My baby: 2010 Honda Fit DX-A Black
Sopus Synthetics and Wix 57356
Genuine Honda Parts
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#4331840 - 02/17/17 09:52 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 12/23/06
Posts: 7272
Loc: Toronto, Canada
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Machine optimal operating temperatures are much, much higher than the temperatures humans feel comfortable with. Hence a lot of people feel the need to lower those temperatures by removing thermostats, bypassing coolant hoses, installing extra coolers. Most of the time, this emotionally driven behavior causes more harm than good.
Edited by KrisZ (02/17/17 09:52 AM)
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#4331851 - 02/17/17 10:01 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 06/28/03
Posts: 5603
Loc: Illinois
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If you want maximum gas mileage then keep it all hot. If you want to not so much heat up your intake manifold then remove the TB hoses. If you have a turbo you are using an Inter cooler to cool down the air going into the throttle body. No sense having the throttle body at 200F or so.
The most popular reason for keeping the TB hot is so the throttle plate doesn't freeze at high humidity, barely open TB(fastest flow past the plate and resulting pressure drop) and temps just above freezing.
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2008 Hyundai Accent 1.6L 5 sp manual hatchback
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#4331857 - 02/17/17 10:04 AM
Re: Why are IAC Valves Heated?
[Re: Linctex]
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Registered: 03/20/06
Posts: 2287
Loc: Canada
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during the course of extreme temperature testing, someone felt it helped drivability in some way It's meant to counter the icing that results from the venturi effect, something that can manifest at ambient temperatures well above freezing.
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#4331860 - 02/17/17 10:12 AM
Re: Why are IAC Valves Heated?
[Re: artbuc]
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Registered: 03/01/07
Posts: 1636
Loc: NE
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No coolant or heating on mopar Throttle Body, most of them have TPS Sensor and the AIS Motor, no heating just power to operate the pintle in and out to meter the air what throttle blade is shut.
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#4331888 - 02/17/17 10:49 AM
Re: Why are IAC Valves Heated?
[Re: Tegger]
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Registered: 12/02/05
Posts: 1128
Loc: West Chester, PA
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during the course of extreme temperature testing, someone felt it helped drivability in some way It's meant to counter the icing that results from the venturi effect, something that can manifest at ambient temperatures well above freezing. This is what I believe.
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