I have the same RMP fluctuation on my 2006 C2S and I wasn't sure if it was normal or not. But after reading this thread, I have one less thing to worry about.

 

FWIW I talked with a friend at the dealership and was told it is a sign of a dirty (carbon) throttlebody. Earlier in the thread - cleaning with throttlebody cleaner should stop it.

 

These are not electric motors. They have cams and valves and idle circuits and stuff. Who sits and watches for fluctuations of a few rpm. You guys need to drive more.

 

Looks completely normal to me.

 

It seems I cross posted - as my vehicle does have an electronically controlled throttle body. Really drive more? that's when I noticed it! I would think keeping your intake clean would lead to higher performance/more enjoyment of driving.

 

Ok, got me there. What I meant to say was: by all means have fun with your throttle body. Just came out wrong.

 

Try taking it for a good bash, to 7000 rpm a few times. That should straighten her up.

 

That's normal. Looks to be a bit of gage variability rather than actual RPM fluctuation.

Idle speed is 740 +/- 40 RPMs anyhow so some small up and down could be ok.

The only time I've seen any real idle speed variability was when the AOS was going out (this on my 2002 Boxster) and then the RPMs went up and down by over 100 RPMs. Another time was when the VarioCam solenoid/actuator were acting up and the RPMS went up and down even more and got so low the engine felt like it was going to stall.

Leave the intake/TB and what have you alone. Do not even buy a can of Seafoam.

All you can or will likely do is make something worse by creating an air leak or gunking up the engine with some "cleaner".

 

And if you must. absolutely MUST (as in OCD can be a pita sometimes) run something through the intake system to address what is essentially a non-issue, I suggest you do it just before an oil change. Without changing oil afterwards you will likely do more harm than good, esp if you are on long oil change intervals.