I just replaced my bad roller rocker and readjusted all valves to zero lash. Started the car up, drives great, no hesitation or anything, no clacking, nothin'...

However, on occasion (not all the time) when I slow down to a stop and pop the car in neutral instead of downshifting, sometimes the RPM's will just kind of float at 1500 for a second or two and then drop back to a normal idle of ~900-1000 RPM. The car won't do it when just revving in neutral.

Is this a valvetrain issue?

 

My car does that sometimes on a stock engine and M6. I think it's a sensor (control) issue. What exactly, I'm not sure.

 

Mine will do that sometimes as well... maybe the IAC ??

 

I replaced mine when I cleaned the TB and it still does it.

 

It is suppose to do that so you have vaccum when braking.

 

my car did the exact same thing, replaced the IAC and problem was solved,