So I have been living with this issue for some time. To recap, CEL was P0010 and P0011. On Christmas Day I changed both intake and exhaust solenoids with new ones I ordered on Amazon. I followed the instructions on this site and everything went well. Except the CEL came back on later in the day and the engine continued with its bucking at idle from 900 to 700(or so) RPM in rapid succession. Plus I thought I heard quite an Model T like engine rattle. Finally I took it to my mechanic. He was overworked and had little time, but kept it overnight. He wasn't bothered by the rattle I was hearing but noticed the bad idle. The car would physically shake a bit when the RPM would go rapidly go up and down. He didn't have any more time the rest of the week to look at it, but asked me where I bought the solenoids and what brand. I hung my head and told him they were YAOPEI, but they got 4.5 stars from 26 reviewers! He suggested maybe I try brand name unit on the intake side since that was problem indicated through the CEL. So I bought a genuine AC Delco GM OEM. It took me 10 minutes to replace. I left the battery disconnected or 30 minutes, then started it up. Instantly I could tell the difference. The rattle I perceived was gone, and the idle purred at a steady 700 or so RPM. CEL has stayed off, <fingers crossed>, and I notice the car drives better in every facet. It didn't drive bad before. My mechanic told me other than the idle it drives great. But it runs even better now.

I guess the moral of the story is you get what you pay for. The exahaust solenoid I originally purchased seems to be just fine. But I suppose when you buy cheap you run the risk of more failures out of the box. On the positive side, I bet if ever have to do this again it will only take 5 minutes! One interesting tidbit: the part number on the bad unit was 12655420. The part number on the AC Delco unit was 12679099. So according to whopper's instructions on this site, the AC Delco was the newer version of the part. I wonder if that was the difference?

 

Just superceded part numbers, there are 3-6 others. You didn't need to do the battery thing those codes clear themselves.