Why are IAC Valves Heated?

Status
Not open for further replies.
Joined
Dec 2, 2005
Messages
1,465
Location
Kennett Square, 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.
 
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.
 
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).
 
The IACV (that's what Honda called it) in my 1989 Accord had coolant piped through it. So, this is nothing new.
 
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.
 
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.
 
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.
 
Almost all throttle bodies are heated by the coolant. First mod I do is to bypass the coolant hoses.
 
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.
 
Last edited:
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.
 
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.
 
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.
 
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.
 
Originally Posted By: SHOZ
Almost all throttle bodies are heated by the coolant. First mod I do is to bypass the coolant hoses.


Some things never change. In my old cars we often blocked the crossover in the intake that was filled with coolant to cool the intake charge a bit.

I had a drag car (400 Firebird) that would actually get the intake pretty cold under certain conditions, cold enough to help power a bit...
 
Old Mercedes or VWs with Bosch K/KE-Jetronic didn't have heated IAC valves nor heated throttle bodies(at least on VWs, the Mercedes K-Jet setups had the throttle body downstream from the fuel distributor/air flow measuring mechanism).
 
Originally Posted By: artbuc
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.


+1 icing ...My honda foreman 400 had an electric plug in the carb to combat icing and the wife's carburated Yamaha had the coolant plumbing. Remember Gasahol can absorb/carry water...
 
The only time I have personally experienced this is back in the early 80's I had a Triumph TR7 with 2 Stromberg side drafts. No coolant hoses but did have the exhaust manifold heater tube and regulator on it for the air cleaner. Which I had disconnected.

So driving down the highway once cold foggy morning the car kept going slower and slower. I finally stopped and figured it out. Just sitting with the engine off heated the sliders up enough to break the frost.

I also put a temp probe just in front of the throttle body on my Gen Coupe once and saw temps below freezing at about 40F, this was when the throttle was closed at high rpm.
 
Originally Posted By: SHOZ
The only time I have personally experienced this is back in the early 80's I had a Triumph TR7 with 2 Stromberg side drafts. No coolant hoses but did have the exhaust manifold heater tube and regulator on it for the air cleaner. Which I had disconnected.

So driving down the highway once cold foggy morning the car kept going slower and slower. I finally stopped and figured it out. Just sitting with the engine off heated the sliders up enough to break the frost.

I also put a temp probe just in front of the throttle body on my Gen Coupe once and saw temps below freezing at about 40F, this was when the throttle was closed at high rpm.


Bought a brand spankin' new TR6 in 1974. Loved that car but it was an electrical/mechanical cluster [censored]! White with blue interior. Nice memory.
 
Last edited by a moderator:
Status
Not open for further replies.
Back
Top