Quote:
Originally Posted by jwick
Just throwing ideas out. Partially for my understanding and partially to see if any trigger some light bulb in your mind that leads us to a solution. I could be completely off but stick with me. So NA it's pulling metered air in from the intake (post-MAF). I would guess the ECU is expecting a certain amount of air to be removed from what it's metering, where in reality (vented) the crankcase is pulling in as much unmetered air as it wants. There is no adjustment for that air not being removed and when you come off throttle it hiccups because it's getting more air than it expects leading to the lean condition. Which is what we see happening.
But let me throw an additional monkey wrench. The GTM kit ties that secondary in pre-MAF, so it has to be something different or in addition to what I stated above or there is something in the tuning that can correct for that.
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You could be right, as the car switches from open loop to close loop it could cause a hiccup until it stabilizes itself. Easy way to try and see if this is causing it is to pull both lines and plug the ports in the intake manifold and idle the car and see what happens. You could just vicegrip the lines to and let the secondary system do all the venting. I am going to try that this weekend and see what the car does.
Is that secondary drawn in pre-turbo? It could be that there is enough vac pre turbo to keep the air being drawn through that system to minimum. But your right the same principle applies in this case as well. Its a head scratcher for sure. Ill try and get some time tonight with the car.