Alright, I know the first reaction is, "that's stupid!", but hear me out at least and then go ahead and say it.
If an MAF car drives perfectly fine, except for a rich idle, then inducing a small vacuum leak and resetting the TB to the desired Idle RPM would, in theory, reduce metered air while keeping the same amount of total air. The result is a lower signal from your MAF which should command less fuel. So long as this is a sufficiently small vacuum leak, then under load in closed loop, your computer will compensate to achieve the desired AFRs, and under maximum load (WOT) the vacuum leak is also sufficiently small enough to have no impact on AFRs, as 1) there's far less vacuum in the manifold at WOT causing a drastic reduction of air flow through the vacuum port, and 2) the proportion of total air from the open vacuum port is insignificant compared to an open 65-75 mm hole (TB).
Obviously, if you had a tuner, you could just change the transfer function or otherwise command a lower AFR, but with the stock computer, would this method be a safe solution? Is closed-loop simply going to return my idle to its currently rich condition? Perhaps it's already doing everything it can to lean the idle out and has reached it's limit...
Ok... *braces against the "you're dumb!" responses*
If an MAF car drives perfectly fine, except for a rich idle, then inducing a small vacuum leak and resetting the TB to the desired Idle RPM would, in theory, reduce metered air while keeping the same amount of total air. The result is a lower signal from your MAF which should command less fuel. So long as this is a sufficiently small vacuum leak, then under load in closed loop, your computer will compensate to achieve the desired AFRs, and under maximum load (WOT) the vacuum leak is also sufficiently small enough to have no impact on AFRs, as 1) there's far less vacuum in the manifold at WOT causing a drastic reduction of air flow through the vacuum port, and 2) the proportion of total air from the open vacuum port is insignificant compared to an open 65-75 mm hole (TB).
Obviously, if you had a tuner, you could just change the transfer function or otherwise command a lower AFR, but with the stock computer, would this method be a safe solution? Is closed-loop simply going to return my idle to its currently rich condition? Perhaps it's already doing everything it can to lean the idle out and has reached it's limit...
Ok... *braces against the "you're dumb!" responses*
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