I've been trying to figure out an issue with my car for a while now. I've searched all over, but can't find the solution.

When my car is warming up, the RPM fluctuates between 1000 and 2000 rpm when under very light throttle. More than light throttle has a bit of hesitation. Car is a 2007 G35 sedan with 5AT and 208k miles.

This only occurs when the car is not quite warm, but not when it first starts up. Once warm the car drives smoothly. I've tried cleaning the throttle bodies, and MAFs already.

Anyone have any ideas?

Edit: I'm not throwing any codes, no CEL, nothing.

 

Recently cleaned the TB? Could be a vacuum leak n

 

Yeah, cleaned the TB but that didn't change anything. I sprayed carb cleaner around vacuum lines to check for an intake leak and didn't find anything. I'll hook up a vac gauge tomorrow to check for dips.

Any chance this could be o2 sensors or a clogged cat? Any way to confirm either of those?

 

Not sure if this was the only issue, but I found this today. There's a giant hole in the intake resonator.

I replaced the factory intake with a super cheap "cold air" intake. I took it for a quick test drive and it seems better, but not completely fixed yet. Do I need to do a reset, or should I just expect it to smooth out over time?

 

If you do the reset it will fix itself immediately .

 

Still having issues. I hooked up a vacuum gauge and got steady vacuum (15 cm Hg), so I think my vac issue is fixed now. Car still drops in rpm between 1000 and 2000 rpm with light throttle.

There's a rattle towards the back of the engine when this happens. Right near the transmission dipstick. Any idea what that could be from?

What else would cause rpms to drop suddenly?

 

In case anyone has this same issue. It looks like this is caused by the VTC during warm up. The fix is buying new VTC covers at > $500 each. Not really worth it given the car is worth not much more than that these days.

 

Interesting. It wasn't a gasket? It was the whole cover? Thanks for replying back (I clearly don't know anything about VTC).