Error 505

Yea I just finished my engine rebuild today and when I was idling it the engine light came on. I ran diagnostics and its error code 505 system Idle failure. What can be the cause of this and how can I fix it. the idle was bad it would go up to about 1800 and then down to bout 1100 and before it used to idle aorund 800.

Also I'm having problems installing my boost controller because the nipples on the controller are a lot bigger than that of the wastegate actuator.

Come on guys what could cause bad idling.

did you remove your honeycombs? Maybe you have a vacume leak? Did you check vacume?

Yea i checked my vacuum its good no boost leak either at idle its 20 hg.
its something else

Since no one seems to have any ideas yet maybe I can help out by saying a little more. I had this problem just before I did the engine rebuild too. So we can eliminate basically evertyhing directly around the engine cause its all been done. I justs assumed this engine rebuild would get rid of it but nope. For some reason I'm thinking something to do with cam's cause those weren't changed.