I have a 2004 Z06. There is a period right after cold start where the engine RPM correlates with the vehicle's speed - when the car is in *neutral*.

For example, if I start the car up and coast down my hill to the stop sign with car's 6-speed in neutral, the car will be at like 1,500 RPM. Then, as I brake to the stop RPMs reduce gradually to about 1,100.. Which I would consider normal for a just-started cold engine at idle. Then after being stopped for a second at the stop sign, the engine seems to fully calibrate and idle drops to normal.

I know it's normal to idle high upon startup as the car's computers calibrate, but I don't get how the RPM could directly correlate with speed unless there was some weird clutch engagement issue going on.. As I coast along, speeding and slowing, the car RPMs increase and decrease like it's an automatic in Drive.

Any ideas what might cause this? It's been happening for a few years but I just want to make sure this isn't something I should look into. I'd hate to be creating some kind of long-term damage to the car. I'm thinking it possibly started when I put a Mantic ER2 single-disc clutch in to replace the stock one? The car has a forged LS6 and an A&A supercharger kit if that's noteworthy.. lol

 

It's likely the way it's tuned plus the clutch weight change, unless you have a significant vacuum leak somewhere. If it were stock it would be easier to guess on potential mechanical issues. But I bet ya a candy bar it's in the tune.

 

I believe the idle issue is either in the throttle cracker or throttle follower values, my tuner took this out for me, as mine was doing the same. Someone here will explain exactly what it is, but when I had cam surge and the rpm drops too, I took it to a really good tuner and now it's honestly all the throttle operation feels like stock, zero surge, no rpm drops after getting out of the throttle, it's fantastic, and it's a hair short of a stage 4 cam.

 

I had an LS swapped car once that did the same thing. My tuner fixed it.