Classic '79 Blazer - idle problem

[mjrhoads]

Need some advise on idle problems with my '79 Blazer.

First of all, this has the original 350 with many upgrades (Edelbrock Performer manifold, RV cam, lifters, springs, roller timing chain & gears).

It has the original Quadrajet (rebuilt & tuned to the Edelbrock after market parts above).

It has good vacumn (EGR & PCV work fine), fresh NGK plugs installed, and timed. Does not burn oil (replaced the valve seals recently), and generally runs strong, except for this recent idle problem.

It seems like a vacumn problem, but I can't find any leaks! Again, this motor purrs like a kitten, when rev'ed up from idle.

But at idle, it lobes like it has a radical cam, and the idle RPM's vary by ~ 50-75 RPM's (which it just recently started doing).

Any idea's what to check next?

[DetroitMuscle]

Adjust the air/fuel mixture and adjust the idle screw a little bit.