cloud and daggar (and any others interested)
I previously owned an 89 gt a serious cam and extensive engine work. when reassebling the engine i used the valve covers that the previous owner had supplied. these vc's had a simple filter element (breather) in the pass vc. I then added a vortech supercharger
. the idle was so erratic after the supercharger install, worse then before. I always attributed this to the wild cam but was perplexed as to why it got worse with the addition of the vortech. well after much troubleshooting i theorized that crankase vacuum at idle with the throttle closed (from the pcv) was sucking a considerable amount of air in through said breather, traveling through the crankcase, up the pcv, and into the intake manifold UNMETERED. this exhibited the same symptoms of a serious vacuum leak. simply removing the breather and placing my hand over the hole in the valve cover smoothed the idle slightly. I was able to tune some of this out with a CraneCams Interceptor but still wasn't right...
Why was it worse with supercharger? because of the restriction the s/c created at low rpms the air sucked through the breather was more aggressive.
just my 2cents