I think the big problem with intake heat soak is if there's a temp sensor there that's used by the ECU to control mixture, and if that temp sensor is significantly affected by the intake temperature rather than accurately measuring the air temp. You can then run lean because the ECU feeds less fuel to what it thinks is hot air. This is pretty likely to be the case with some cars but not others, based on the engine management scheme.
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that might be the bigger issue. on my car the intake manifold is right behind the radiator, along with IAT sensor.

aem on air inlet heak soak;
http://trucks.aempower.com/press_eve...ail.asp?aid=15