Why are IAC Valves Heated?

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My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.
 
Originally Posted By: artificialist
My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.


What about the IAC valve?
 
Originally Posted By: artbuc
Originally Posted By: artificialist
My understanding was that by preheating the throttle body, it would heat the air/fuel mixture enough to help it vaporize in cold weather. That would reduce smog during cold weather. This is one of the reasons that many carb and TBI V8 engines had a coolant passage inside the intake manifold underneath the carb or TBI unit. Also, I think heating the throttle body was also an alternative to using air cleaners which had snorkels routed over the exhaust manifolds.

This was less of a problem with inline engines which had the intake and exhaust manifold on the same side of the engine. Radiant heat rising from the exhaust manifold was often enough to aid in preheating the cold air/fuel mixture.


What about the IAC valve?


Heating the IAC valve would still heat the air fuel mixture at idle to reduce smog at low temperatures.
 
Originally Posted By: KrisZ
Most of the time, this emotionally driven behavior causes more harm than good.


lol.gif
 
My 8HP Tecumseh Snow king engine has a heated carb I think.
On most engine, There is not enough surface area in the TB to provide significant heating of the air column. I would most assuredly say it is to prevent icing at the tb at idle and light throttle where there is a lot of gas cooling due to a "refrigeration cycle" occurring around the throttle. The IAC is usually nearby, and the IAC is a throttle bypass subject to freezing as is the main throttle.
 
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