Hey everyone. I first wanted to say thanks to everyone who posts on here as I've learned a lot from this forum and I am very happy with my mod choices.

Car:
2009 G37 Sedan RWD 7AT

Mods (in order of installation):
-Grounding kit
-Stillen Gen 3 intakes
-Fast Intentions RHFC
-Tanabe axle back exhaust

The issue:
I get some pretty bad vibration, shaking and sometimes a yerk while in D or DS at stoplights/idle. This usually only happens whenever the car has warmed up. My RPMs sit almost right at 600. It will fluctuate ~100-150. When it fluctuates lower the vibration is worse. The vibration does not exist in P.

Things I've checked:
-Throttle bodies were clean when I installed the intakes about 6 months ago
-Intake filters are clean
-I checked for leaks in the Gen3 intakes and on the HFCs

What I believe is the issue:
I first noticed it after I had the RHFC installed and it seemed to get worse over time (maybe mental). After I installed the Tanabe, the vibration is worse (which does not make sense to me). I know the brace from the original cats were removed, so today I had a chance to get under the car to see if I could find anything. I had my wife keep the car in DS while I was under the car. All connections looked good but no vibration. I got out and revved the car ~10 times. At this point the vibration showed up. The RHFCs and the pipe connecting to it (mid/y pipe?) were vibrating violently and quickly. Where the RHFCs connect to the headers, it did not look like the vibration was very bad. Let me know if you need more detail.

I would really appreciate anyone's feedback on what could be causing this, any suggestions for a fix or if there is anything else I should try I am open to anything!

Thanks guys

 

This description above was little too long winded so the summary is:
I get sometimes violent vibrations after installing my RHFC (which I really love).

I am planning on getting a muffler shop to look at it and will report back but before I do I have three main questions I hope someone can chime in on:

1. Do you think adding a brace to the RHFC will help with the vibrations (they get pretty bad/strong sometimes)?

2. Do you think a lean AFR could be causing the dips in RPM and causing the vibration?

3. Anyone experience anything similar? I want to determine the root cause of the vibration.

I just noticed I could have put this in the "Intake/Exhaust" section, woops! Please move, if possible/recommended.

 

I experience the same thing on my 2008 G37S coupe 6MT.
I had a shop check out the intakes and they said it was a bit loose, then refitted it for me. They didn't mention anything about the throttle bodies though but I'll look into that next...
I really don't know what it is either, and I've had the problem for a while now. It happens during normal driving and pretty much 90% of the times when I come to a stop sign or red light... Like you said, after it has warmed up, I guess.

There's a similar threat in the "G37 Coupe" section about RPM dipping while idling. A few more people are having this problem.

 

Did the refitting of the intakes help any? Do you have after market intakes?

I talked to a local muffler shop and will be getting some diagnostics run hopefully this week or next. Their initial thought was a possible leak or bad AFR.

Nice, thanks for pointing out the similar tread.

 

I'm having the same issue but I notice it with the AC on- the RPMs dip and I hear a rattle. I was thinking maybe it had to do with the AC compressor or perhaps something loose. Keep us updated if you find out the root cause of the noise. I'll do the same.

 

I've made some progress and learned some more about the vibration.

Over the weekend I cleaned my intake filters, which were surprising dirty after only 11k miles. This seemed to help the vibration some (30% better I would say). I then cleaned the MAF sensors and the throttle bodies. This also seemed to help out a good amount as well.

My idle now only fluctuates 25-50 rpms when in drive. The vibration/shudder only comes when the rpms hit 600 but then if it moves up or down and it will be gone.

The story continues...

I have worried about my AFR and running lean so I decided to bite the bullet and get a Uprev tune. I decided to go with Uprev etunes over dyno for numerous reasons. So yesterday I flashed it with a base Uprev tune. I hope that getting my AFR in check gets ride of the rest of the virbartion. The last resort would just be to set the rpms higher/lower so they do not hit the "vibration zone" I now have.

One last comment...I believe even more vibration would be removed if I got the OEM catalytic converter base installed again. It was removed for the FI RHFC install since they do not use it.

I hope this is helpful to someone.