Low temperature but high humidity. Say when it's foggy and just around freezing, like when you have snow on the ground but a warm front with moist air pushes through, all that humidity turns to a thick fog bank but it's still in the high 30's maybe low 40's. That's when throttle icing is likely to happen. Also at higher altitudes as well where you can have cooler air with higher humidity. You can use the same charts pilots use.

toyota makes cars that are sold all over the world. its cost effective to make them all the same way. chances are i wont see those conditions in So Cal. but if i drove up to North Dakota, i just might see those conditions.

My opinion is that the possible gain is so tiny and unlikely that the effort isn't worth it given the potential for things going wrong.

My idle is fine. And my car hasnt exploded.

Yes, and you live in a generally very warm and dry region. If say you lived north of the mason-dixon line and drive the car in the fall, winter, or spring, or take it on trips to different elevations and areas of the country I'd suggest against this.

Actually last winter we got a good deal of ice and I had no problems. But yeah, if I lived in an area where I feel this would be a concern I would of left it stock.

The odds of it happening are fairly slim since heat is conducted through the head, into the intake, and to the throttle body anyway, the coolant just warms it up faster when it's cold outside to make absolutely sure it won't ice. Once the whole engine and engine bay is warmed up then that coolant flow doesn't matter really, which is another reason why the bypass makes little to no difference since it would only possibly lower intake temps when the whole engine is cold, unless you have a non heat conductive intake manifold or throttle body spacer.

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Bitter and Smaay. . . thank you for helping me to understand. I was gone all day today but was very happy when I returned to find that Bitter had cleanly defined the conditions under which throttle icing can occur, conditions that make sense to me as the only way it COULD POSSIBLY happen, given the laws of physics, and Smaay followed up with a rationale from Toyota's point of view. Since becoming a member it's been easy to see that the both of you are quite expert and skilled (relative to many others) in auto mechanics/engineering, whereas I am just learning, and normally I accept what you say without question. This time I needed more pinpointed attention to my questions than you offered until I challenged the fuzzyness of your answers. Now I fully believe that my Celica's throttle may very well freeze up under those precise conditions, so I should always be self-aware and ready, prepared with memorized actions to take to avoid a potential disaster should it ever happen to me.

Let me remind you of the patent I referred to earlier as a way to help those people on the fence about shunting their TB coolant flow. By letting engine coolant flow through the TB at start up, then when the engine is warmed up, shutting it down, the patent holders claimed that they were able to shorten engine warm up time from 250 seconds to 178 seconds -- the main object of their patent was to speed up the process of engine warm up -- and they cut out approximately 30% of the engine warm up time. They considered that a very positive advance in automobile technology. With Celicas that do have coolant flowing in the TBs, you realize the same speedup in engine warm up time. Defaulting that coolant flow not only subjects you to the possibility of finding yourself in a bad situation due to throttle freezing (most likely prior to reaching normal engine temperatures), BUT you also loose the advantage of a faster warm up.This all suggests that we should NOT do what this thread was begun to show how to do. For me, it is a null issue because there is no coolant flowing in my TB (94 Celica ST).

This post has been edited by Langing: Sep 13, 2014 - 9:53 PM

I'm about to reconnect mine onto my TB.

I'm only somewhat worried that it'll increase my IATs, since I'm boosted.

I'll bet it makes no discernible difference.

this is what I was unsure of at first, but now I'm convinced that the actual idle control is just by the computer. and the bi-metal spring will just break it open if it were to freeze up.

yet I really doubt this will effect the incoming air temp much. it only warms up the bottom part of the throttle body and the air passing through there is moving too fast to be warmed up much I'd think.

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When air is 'colder' it is more dense, and thus contains more molecules of oxygen per unit of volume than warmer air, so more oxygen is available to the combustion process when intake air is colder. Also, the step-function reduction in air pressure as it moves through the throttle body into the 'vacuum' of the intake plenum is said to lower the air temp. This is in line with the statement by 4-eyed-freak. Can anyone point me to a good technical discussion of the dynamics of this process that explains it in more specific detail that spells out how much heat a warm throttle body adds to intake air temp, and how much cooling is provided by the pressure drop, along with other relevant info, like how fast is heat is being transferred from a warming block to the throttle body conducted through the intake 'pipes', and specifies what is the ideal air temp as it enters the cylinder?

How do these dynamics change as engine moves from cold to warm, and as throttle moves from idle to WOT?