I have a 09 G37x with gen3 and berk HFC mods. Every time i'm stopped while the car is in drive (does not do it in reverse) it shakes/pulsates. The magnitude of the pulsates varies and usually its much more noticeable during cold starts and cold weather. During the winter when this occurs it felt like it was the brake booster because I could feel it through the brake pedal and the problem is eliminated when the car is in neutral. The magnitude also increase when there is more load on the engine (using windows motors).
I recently brought my G in to a dealer (still under warranty) and they said my HFC is causing it to idle rough and the ECU saids my car is running lean. I feel like my dealer is using my HFC as a scapegoat since the diagnosis came so quickly (within a hour)
Is anyone else having this problem?

 

I haven't read of other's on this thread having this issue. Have you looked into your throttle body's being dirty? There's a DIY on this thread showing how to clean them, thus correcting rough idles.

 

did you ever figure out what this was?

My car seems to be doing this as well. The idle isnt dropping but you can feel the car shaking. I actually notice it when in neutral and completely stopped only.

 

I noticed exactly this immediately after I installed my FI RHFCs. I'm not sure if it has to do with the tone of the exhaust vibrating my cabin, or the fact that most HFCs/Test pipes don't bolt down to the underbelly of the vehicle like the OEM cats do.

I feel this only when I come to a complete stop with my foot on the brake. I feel it most coming through my seat and shifter. I don't feel much in the brake pedal or steering wheel.

toughcookie if you don't have any exhaust modifications, I would check your throttle bodies and clean them. It will definitely help if you haven't done it before.

 

I agree with the throttle body cleaning, especially if you're running a long tube CAI. I too have the FI RHFCs, but no such issue after 20k+ miles of them being installed. A TB cleaning is inexpensive and only takes less than 45 minutes.

 

Yea i havnt done anything to the exhaust. Im going to try to clean the throttle bodies this week