Get a vibration at 750rpm idle, but not at 850rpm idle?

[MC Hammered]

The tune I have idles great at 850rpm.

I wanted to lower the idle, so I set it tonight to 750rpm and I get a very noticeable vibration. Touch the throttle to raise the rpm a bit and the vibration goes away.

Does anyone have any idea what would cause such a vibration just from lowering the idle speed 100rpm?

I am running AKG poly motor mounts if that makes a difference.

TIA for any information.

[pazi88]

Engine specs?

But with poly mounts you will feel the engine shaking.

[MC Hammered]

USA s52 engine, stock injectors, M50 intake.

[Northern]

I'm running the FX Stage 3 flywheel/clutch combo, Condor mounts, and some other odds and ends.

As of this spring I noticed that my idle was sort of rough(already bumped to 800RPM). Almost like a misfire every 2 seconds or something (which it might be, still haven't looked into it too much)

Bumped the idle up to 900RPM, seems a lot better now, but still feel a little bit of something going on.

[328ijunkie]

I put most swap tunes at ~820. Happy medium. lower and you can get severe FW chatter and or NVH.

[MC Hammered]

I put most swap tunes at ~820. Happy medium. lower and you can get severe FW chatter and or NVH.

Thanks for this feedback. So it is the FW that is creating this harmonic?

[328ijunkie]

FW plus a number of other things.