Check me if I'm wrong but I believe walnut blasting only applies to turbocharged engines.
EDIT: Sorry, I was looking at the ZHP in your sig. So I'm not sure why all the talk about rough idle - never had any rough idle in mine whatsoever. Had mine walnut blasted at 120k miles, and my indy said the valves were the worst he'd ever seen, and he'd seen some bad ones
. But the walnut blasting can make a significant difference in terms of smooth acceleration.