I have a SBC with 11.5 :1 compression, which lately misses at idle but clears after 4000 or under load. Runs strong. Under full throttle it smokes blue, it has for years.
But I can't tolerate the idle miss anymore so I checked the rockers for proper adjustment, they were fine. I replaced the intake gasket, no difference.

Today I started checking compression, and number four plug was black and only 155 lbs whereas 3 others all have 190psi which is what all the cylinders had a few years ago. I figured I found the culprit and the other four plugs are hard to get at so I thought I'd throw this out.

Would a lack of 35 psi on one cylinder cause a total misfire or do I possibly have a bad spark plug wire and maybe that cylinder hasn't run proper for a while and caused the compression to drop?

So then it is either a valve or rings, short of that I am stumped.

Oh, I have MSD 6AL plus 3 step Retarder.