[MikeK]

There have been at least two posts so far in this thread suggesting an exhaust back-pressure problem. The symptoms certainly fit an intermittent occurance. I could see this for two reasons in an A: 1) an accumulation of those dreaded exhaust manifold seal rings down the pipe, sometimes jiggling into a blocked configuration. 2) Big rust flakes accumulated inside the muffler. When running they randomly fly up and block some holes, eventually too many. After sitting they settle, all is normal 'till it repeats.