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#4331641 - 02/17/17 04:09 AM Why are IAC Valves Heated?
artbuc Offline


Registered: 12/02/05
Posts: 1114
Loc: West Chester, PA
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]
Linctex Offline


Registered: 12/31/16
Posts: 4741
Loc: Waco, TX
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]
sdowney717 Offline


Registered: 10/01/05
Posts: 299
Loc: Newport News, VA
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]
supton Offline


Registered: 11/09/08
Posts: 11389
Loc: NH
Originally Posted By: sdowney717
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]
DBMaster Offline


Registered: 09/18/12
Posts: 5250
Loc: DFW
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]
ARCOgraphite Offline


Registered: 05/17/09
Posts: 11655
Loc: N.H, U.S.A.
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]
The_German Offline


Registered: 01/13/17
Posts: 128
Loc: Montreal (West Island), Ile Pe...
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]
Rand Offline


Registered: 08/20/03
Posts: 12352
Loc: NE,Ohio
Originally Posted By: The_German
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]
SHOZ Offline


Registered: 06/28/03
Posts: 5456
Loc: Illinois
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]
The_German Offline


Registered: 01/13/17
Posts: 128
Loc: Montreal (West Island), Ile Pe...
Rand you are correct I didn't read it right.
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#4331840 - 02/17/17 09:52 AM Re: Why are IAC Valves Heated? [Re: artbuc]
KrisZ Online   happy


Registered: 12/23/06
Posts: 7058
Loc: Toronto, Canada
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]
SHOZ Offline


Registered: 06/28/03
Posts: 5456
Loc: Illinois
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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#4331857 - 02/17/17 10:04 AM Re: Why are IAC Valves Heated? [Re: Linctex]
Tegger Offline


Registered: 03/20/06
Posts: 2287
Loc: Canada
Originally Posted By: Linctex
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]
VNTS Offline


Registered: 03/01/07
Posts: 1631
Loc: NE
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]
artbuc Offline


Registered: 12/02/05
Posts: 1114
Loc: West Chester, PA
Originally Posted By: Tegger
Originally Posted By: Linctex
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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