Thread: Knock at idle?
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Old 09-24-2009, 12:13 AM   #5
Scooby Specialist
Member#: 156973
Join Date: Aug 2007
Chapter/Region: International
Location: Adelaide, Australia
2002 ADM WRX STi
STi Black/Blue


Originally Posted by TurboSetch View Post
Knock learning is not applicable at idle with stock tables on that car.
It depends what load is while idling. If the load is above the minimal knock correction thresholds, then knock correction will come into effect.

From my own experiences, knock being "detected" at idle is generally from one of two things:
  1. Noise - intercooler piping, uppipe, dumppipe, catch-can (or anything else metallic) touching/bumping/hitting against something else metallic.
  2. Low timing* - as you lower timing you increase EGT, as EGT increase, combustion temps increase, and that can cause pre ignition. Also at idle you have very low VE and slow combustion speed, and the lower the VE and combustion speed, the higher your advance timing should be.
* Don't just go increasing timing stupidly or you can and will damage your engine.

The following suggestions are for low load and low rpm knock that doesn't seem to go away when lowering timing

My advice is to open a stock ROM and compare the base and advance timing tables to your current ROM's tables. Specifically, compare the values at and around the RPM where the ECU is registering knock when you are idling (around <0.3 load and <1200 rpm).

Then set your current ROM's values to whatever the stock ROMs values are in those cells and smothen the transitioning cells - flash the edited ROM and see if the ECU is still detecting knock (also check the transition load/rpm points while logging to ensure the changes haven't induce new knock.

Saying all that, if setting knock back to stock values at those low load and rpm points doesn't fix it, then it is most likely noise - so check and tighten everything in the engine bay.


P.S. I want to reiterate that ppl shouldn't just start increasing their timing, as doing so without carefully logging and evaluating the changes can cause knock and kill your engine quick.
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