97 blazer 4.3 runs great at high revs, p0300 at idle only
 

Just put the engine back together after replacing a cracked head. Now I'm getting rough idle and misfire code p0300 only at idle, as well as the CEL flashing. If i raise the revs, the flashing stops. Also if I start the truck and keep the revs up, the CEL never comes on and seems to run smoothly. I have triple checked the crank to dist. timing and its dead on the marks. Any thoughts are appreciated. Thanks!

fuel pressure key on is about 55, and engine on it is at 60, and holds steady for a few min after shut off.

also tried carb cleaner at vacuum lines, no change in idle speed. it did smooth out some with carb cleaner into air cleaner tube.... Sorry for the multiple posts, but it won't save my edits ...

same issue
 

Im hunting down the same problem let me know it you find anything. I'll do the same.

Stuck EGR valve?
Dirty/hanging up idle air control motor?

Those are about the only 2 vacuum leaks that spraying the vacuum lines won't help identify.