I just finished breaking in my ZZ4. It runs great an idles with a slight lope. I am currantly working on my prom tune. I hooked a vacum gauge to the plenum and noticed a slight deflection on the vac gauge. It is not erratic it goes from 17 in. to 18. in back an forth. It stays at 17 for 5 to 10 seconds and then to 18 for 5 to 10 seconds. What would cause this? Posibble vacum leak.

Thanks Tom

Is the idle varying slightly as the vacuum changes?

In any case, if it's not erratic and it's only changing 1", I wouldn't worry about it

The idle is not realy varying, just 25 to 50 RPM.