So im pretty sure i did everything right, used the cam gear from the Z6 head got it all timed up nice and beautiful and readjusted valve lash, no clicking whatsoever . The problem is as follows; motor will start and idle beautiful all day and rev up like a dream. When I let off the throttle the RPM's drop below 500 and it hesitates/stumbles for a 2-3 seconds then resumes the idle. I am rather baffled as to what is going on, possible fuel pressure regulator? MAP sensor? Whats going on?

 

Is the CEL ON?

Have you tried cleaning the IACV (see forum DIY section)?

 

no the check engine light is not on, i will check up on the IACV though