Here is a post I wrote on another website regarding the P0299 a couple of days ago:
"Before anyone gets carried away I will say that this code is a result of using larger than stock aftermarket turbos.
Or that this code only shows up when the larger turbos are used.
This does not mean there is something wrong with the turbo as some may to try to say. Its just a fact of life once you change to an aftermarket charger. The engine is setup to run a stock unit and when its sensors dont see exactly what it likes the ecm kind of freaks out.
I used to get this with my 66 turbo that I had many moons ago on my 04. 5.
It wasnt really a big issue or anything to worry about but I did keep my bullydog programmer at the time with me in case I had it pop up.
Funny thing is I had the code pop up on the same part of the interstate the same day. There happend to be some hills around.
As far as I could figure out there was no magic fix for this issue. I will say though after I changed turbos I havent had it pop up again.
The little solenoid slug will not fix the issue, plugging in the stock turbo solenoid will not fix the issue. The issue is not the map sensors fault either. I also had a "boost fooling" box so that corner was covered and my stock solenoid for the stock turbo was plugged in (as is still is today).
I could also hit 50psi without issue... . so boost was being achieved just fine. "
**to clear the 0299 you will need a SMARTY, BullyDog or similar downloader that will clear hard codes the generic code scanner wont clear.