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Engine sound with different throttle actions (warmed up)

Engine warmed up, this is the sounds when:

  • consistent throttle to about 4000rpm
  • flat-to-the-floor throttle from idle
  • flat-to-the-floor from about 1500rpm.

The two consistent observations I have are:

  1. When the throttle is released the revs drop to around 1100rpm and then after another 4 secs so drop to the 750rpm idle.  This response seems a little slow?
  2. The distinct ‘gulp’ and hesitation when the throttle is floored.  I understand induction noise, but this is almost as if the butterfly isn’t opening smoothly?  Or could this be a failed intake manifold (as some have suggested)?

I’ve tried to replicate the ‘screwdriver to the ear’ technique but placing a dictaphone directly against the throttle body components – all at idle – included the nearby injector rail just to highlight that the ‘ticking’ it is not the injectors.  I really don’t know enough about these to know what they are supposed to sound like…..

 

Just for interest I’ve added some images of the LPG system below as well.