What kind of benefits are you expecting from this IM swap?
I never swapped the intake manifold over. I wasn't expecting any performance benefits, I just didn't feel like taking the Japanese spec IM off from the new engine if it didn't to. I compared both the US and Japanese Intake Manifold side by side, they looked exactly the same other than the throttle cable bracket, fuel rail and some sensors that needed to be transferred over. The japanese one looked cleaner and in better shape, that was basically my reason by keeping it on. The shop i bought the engine from, kept suggesting that I "needed to change it over and the exhaust manifold, to make the the swap to work; because of fitment issues and Check Engine Light codes", which I didn't do.
But at the time, I was assuming the fluctuating idle issue was due to the internal design of the Japanese IM. I began thinking to myself "maybe I should've swapped it over the US IM from my original engine". But with some research and advice from reputable master mechanics, I figured it was just a vacuum leak from the PCV valve and the IACV valve needed to be cleaned more thoroughly.
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