98 gmc 6.5l p0238 code
 

I'm having a hard time finding my problem with this p0238 code. To start off before this code came up my alternator went out replaced it and soon after a p0236 code came up replaced the map sensor and now i'm gettiing a p0238 code. In the morning it starts out normal then about 20min in the drive the truck starts losing power and black smoke. I hook my code reader up as im driving and keep erasing code and runs fine. checked my vacuum line and turbo actuator and seams good. I'm thinking might be something wrong with the PMD what wanted to see on thoughts first.