Re: EDL-2098 Package High Idle?
As Tom said, with that high of an idle you are already in the centrifugal advance curve and not on the idle curve... Same problem I had with a similar cam in a 327, also, if you're running vacuum advance, the idle vacuum is probably too low for the can, deploying the vacuum advance in and out at idle, this would cause fluctuating timing as well as a dithering rpm.
20+ degrees at no lower than 800rpm should be right.
I'd shoot for 900-1,000 idle at operating temp, don't even try to tune it if it's cold, have to get it to operating temp or your idle speed will jump right back to where it's at now if not.
The only Mustang I'd ever own is a Fender.
'68 333" Camaro
'14 5.0 Mustang