noisy idle noise - "diesel" like sound
 

Hello again to this great community!

I decided to write here for an issue im having lately. My 2.7 (2003) boxster engine is doing a "knocking" sound on idle.

About the noise:
- Almost Irrelevant if warm-cold engine.
- It Reminds me of a diesel engine car sound (:confused: :barf:)
- No CEL or anything related, spark plugs/coils/oil new

Only thing im a bit guilty is that the sound started happening when i switched to 95 Octane, but maybe its irrelevant ?

No idea of the Serpentine belt condition by the way.

Thanks to All!

My water pump sounded like you describe when the bearing started to go. Pull your belt off and check the WP.

Perhaps lifter knocking
 

My CS developed a lifter noise while idling and a friend of mine (Porsche specialized shop) suggested to try Liqui Moly "hydraulic lifter additive" which I used on the next oil change (LM 5-W40) and it helped a lot to reduce the lifter noise, you may want to try it.

I had the “diesel” noise late autumn/early spring - extremely annoying sound. Proved to be the servopump and the generator making noises at idle. I did not do the replacements myself but according to my independent technician it was not a straightforward job.
Mine is 2003 S with 190.000 km on the clock - now spinning like a cat again.

Sounds like the water pump. Mine made the same noise right before it started
dumping coolant.

Have u tried opening the engine access behind the seats? try to use a plastic tube and use it to hear each part of the engine where the noise/sound is coming from.
Water pump, idler pulleys, alternator, power steering and AC motor.

My waterpump went down 5 years ago at about 125.000 km - sound maybe similar but much more aggressive - and if the sound came “lately” it does not correspond with my wp experience.
Mine was: Sound - leak - wp bonkers!
But of course it is worth checking everything,