engine vibration at 1900 rpm only 987/997

[mayes911]

i have a 2008 cayman s low mileage well maintained car,and whilst sitting at some traffic lights today i decided to increase the revs slightly and noticed a vibration/lumpeness at dead on 1900rpm but smooth either side of this rev range the thing is i have never noticed this before in 3 years of ownership.the car is running fine and no other problems.is this normal or am i just being paranoid???

[mollytherocker]

I seem to remember a thread about this very thing on 997's recently?

'They all do that sir'?

MTR

[Rockster]

mayes911 said:

i have a 2008 cayman s low mileage well maintained car,and whilst sitting at some traffic lights today i decided to increase the revs slightly and noticed a vibration/lumpeness at dead on 1900rpm but smooth either side of this rev range the thing is i have never noticed this before in 3 years of ownership.the car is running fine and no other problems.is this normal or am i just being paranoid???

Almost certainly a bit paranoid.

An engine when rev'd like you did will exhibit some bit of vibration even lumpiness at various places in its rpm range. Most owners do not notice this because they do not do what you did and the vibration/lumpiness isn't muted maybe not even present when the car is moving and the engine passes through these various rpm ranges.

The engine controller will through the VarioCam system cause the intake valve timing to change and if the car is equipped with VarioCam Plus (which IIRC the 2008 Cayman S has) then the engine controller also varies the intake valve lift as well and around 1900 rpms is ballparkish for when (at the low rpm range) the timing and lift would be varied.

I do note you state the car is a low mileage car. So there's a slight possibility an engine mount may be bad.

So, it wouldn't hurt to visit a qualified shop and have the mounts inspected just in case.

Sincerely,

Rockster.

[bobsan]

it's all over, engine's about to let go, sell immediately

[mayes911]

Rockster said:

Almost certainly a bit paranoid.

An engine when rev'd like you did will exhibit some bit of vibration even lumpiness at various places in its rpm range. Most owners do not notice this because they do not do what you did and the vibration/lumpiness isn't muted maybe not even present when the car is moving and the engine passes through these various rpm ranges.

The engine controller will through the VarioCam system cause the intake valve timing to change and if the car is equipped with VarioCam Plus (which IIRC the 2008 Cayman S has) then the engine controller also varies the intake valve lift as well and around 1900 rpms is ballparkish for when (at the low rpm range) the timing and lift would be varied.

I do note you state the car is a low mileage car. So there's a slight possibility an engine mount may be bad.

So, it wouldn't hurt to visit a qualified shop and have the mounts inspected just in case.

Sincerely,

Rockster.

thanks for your reply Rockster

bad engine mount how do you mean?surely if it was a bad engine mount would you not notice at other times?

[Rockster]

mayes911 said:

thanks for your reply Rockster

bad engine mount how do you mean?surely if it was a bad engine mount would you not notice at other times?

Bad in that the rubber inside the mount bracket (casting) cracks and the engine is no longer supported properly. The engine will not fall out of the car but in not being supported properly 'strange' vibrations can come and go, the shifter might feel a bit like it is possessed and so on.

Or you might not notice a bad mount at all. I took my Boxster in for something (I forget what now) -- this was several years ago -- and in the course of checking out the car the tech found the front engine mount rubber was cracked -- I could see it when he invited me under the car for a look -- and I went ahead and authorized him to replace the mount.

I do know had the tech not shown me the bad mount I wouldn't have guessed it was bad from the way the car was behaving.

Afterwards while I wanted to note an improvement, the absence of some heretofore unexplained behavior (vibration, or ?) I didn't. As best I could tell the car's behavior was unchanged.

But not all who've gone through a bad motor mount report the same thing. Some have reported noticable changes and for the better after a bad mount was found and replaced.

Sincerely,

Rockster.

[SilverstoneSid]

I have the exact same issue on my 997, but at 1800rpm.

Replacement of clutch and flywheel made it a bit better, but did not cure it. Running a short ancillary belt confirmed it was not the alternator, PAS or A/C pumps. I asked them to check mounts and they claimed they were OK also. There was no misfire or lumpiness in the engine running when checked on the diagnostics.

Fine when cold, gets worse at it warms-up, but gets better again when fully warm. Must be a fundamental resonance in the engine / gearbox and engine mounting system.

I'm now ignoring it and avoiding driving at this one engine speed.

[Rockster]

SilverstoneSid said:

I have the exact same issue on my 997, but at 1800rpm.

Replacement of clutch and flywheel made it a bit better, but did not cure it. Running a short ancillary belt confirmed it was not the alternator, PAS or A/C pumps. I asked them to check mounts and they claimed they were OK also. There was no misfire or lumpiness in the engine running when checked on the diagnostics.

Fine when cold, gets worse at it warms-up, but gets better again when fully warm. Must be a fundamental resonance in the engine / gearbox and engine mounting system.

I'm now ignoring it and avoiding driving at this one engine speed.

Could be due to the DME modifying the intake valve timing and intake valve lift, along with fuel injection pusle widths and whatever else the DME can or could modify as the engine warms up. The intent is to lower emissions and to accomplish this smoothness may be sacrificed, for a bit.

One probably only notices it because the engine is so darn smooth other times.

Sincerely,

Rockster.