Quote:
Originally Posted by ArtS
Has there been any agreement among FRS/BRZ owners as to the cause of the well reported "transmission rattle" when slowing down in neutral? I've seen all kinds of theories suggested here - engine valve noise, fuel pump noise, exhaust noise, piston slap, etc. I think its in the transmission/clutch because when the clutch is pushed in the noise stops immediately. It only happens for about 2-3 seconds at about 700 rpm, clutch out in neutral. What is the best educated guess to what makes the noise???
ArtS - 2015 FR/S manual tranny
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When you coasting to stop (zero throttle) the ecu shuts off fuel injectors ( fuel saving) and the momentum of car keeps engine turning, at some point arround idle rpm the ecu will turn on fuel injectors to keep engine rpm arround idle rpm. The noise is just backlash in drivetrain as this occurrs, especially in combination with airconditioner switching.
You can alleviate the issue with tuning to bump idle to 750 and switch to full direct injection mode at low loads, instead of combination pi\di, this allows ecu to manage idle stability better.