I picked up my first Z over the weekend, a 2008 350Z HR. Initially, I wasn't aiming for a tuned ride with aftermarket upgrades, but given the market and the limited selection in my area and the neighboring cities, most options were barely roadworthy. Seems like tuner cars dominate the scene around here.

During my inspection, everything checked out except for some cable fraying that could benefit from some heat shrink.

Took it for a spin, and man, the exhaust makes it sound like a racecar—too loud for my taste, to be honest.

Now, here's the problem:

The next day, on a cold start, I noticed an issue that didn't come up during the warm start when I first checked it out. There's a clear idling issue. The previous owner mentioned it was tuned using Revup and had been running on E85. He said switching to premium wouldn't be a problem but warned me the fuel mix might be off until I've run through a few tanks to even it out.

This is my first time dealing with a tuned car, and I want to tackle this idling issue head-on.

Should I dive into inspecting the parts myself, or should I consult a local tuner for their take first?

I'm trying to decide whether to start with my usual mechanical/electrical checks or go straight to a professional tuner.