Purchased an ex demo IS350 F Sport and love it! It's my dream car came true. But I have a few questions:
1. I'm experiencing a slight vibration throughout the car when idle. It happens after a cold start and when the engine is warmed up. Every minute or so the vibration or shudder increases in intensity for a few seconds. It's not bad but certainly noticeable. My guess is the air con but it also happens when the air con is off. Is this normal?
2. How noisy is the engine during idle? Is it whisper quiet or can it be heard? I can hear the engine in the cabin and again it isn't bad i can certainly hear it.

I might just need to realign my expectations and get some opinions because my previous car was a Renault Megane and it was whisper quiet with no noticeable vibration. Is the engine noise and vibration normal for the IS350's v6 engine?

 

I think it's the 250s that have the carbon issue cause mine is like that. But the 350s might be have it too, someone else chime in
but I use seafoam every now and then to help clear it out

 

I thought the direct and port injectors would prevent carbon build up or does it just minimize the chance? The car has only done 4300 miles.

 

I'm not completely sure. I know the 2IS had the same issue. It's pretty annoying to have but I personally use seafoam every oil change to help with the issue. Might have a shop clean out the carbon maybe yearly

 

The 3.5L doesn't really need cleaning if you use top tier gas. Carbon buildup is non existent due to the port injection. The only issue with the 3.5L is the lack of low end grunt so you feel the need to wring her out often.

 

I have an IS 300, which has the same 3.5L engine. I'd say at idle it's quiet, but it's more audible than in some cars I have driven. I had a rental Sonata recently, and it was nearly silent when idle. Even below about 3500 RPM when moving, the engine should be relatively hushed in the IS, aside from a slight whine sound which is also present on the GS 350.

Keep in mind, the 350s and F Sports have the intake sound generator, which means the engine is generally louder in the cabin than in other cars. It adds to the sportiness of the car.

 

Hi, neighbor , it is normal ! just enjoy driving it don't worry.

 

Thanks everyone. That puts my mind at ease somewhat. I ran some more tests and at idle the revs hover around 620. The vibration occurs every few seconds consistently and when it happens the revs drops to 610 for 2 - 3 seconds then go back up to 620.

 

There's a slight ticking sound at idle which is normal with direct injection engines.

I get that odd stumble too upon cold start (not when warmed up though), but I think it might be a direct injection thing, as I recall newer Kia 3.3L products I drove had that same stumble.

You bought a demo, which means it was probably beat senseless on test drives or by head office staff who know it isn't their car (but I don't think this will lead to long-term issues, don't worry too much).