I have an early 2004 Heritage XL with the 4.2 v6. It has been making a whistling noise lately when it changes to lower RPMs. In one day, it started missing so bad, It now hardly will get to 45, . It sort of acts like it did when the intake runner control motor was bad. The new one still makes a whirring sound, which I read was a self test, so I think it's still good. Codes are P0174, P2195, P2197, P0456, P0171, P0316, P0306. I could use some input to know where to look. Thanks.

 

couple indirect suggestions:

if you really have a heritage (04) model, then it is essentially an 03. you may find that the 10th gen forum will have more members familiar with your truck.

when you have a “bundle of codes”, consider posting both code #s and their definitions… no reason to ask everyone to search them out too.

 

List the codes, replace the "isolator bolts" somebody decided they need to call those intake bolts with the rubber washers isolator bolts
Remove upper plenum, replace lower plenum isolator bolts
That fixes most of those Heritages with the 4.2, doing what yours is doing

 

Thanks, that is true. Built in May 2004. I'll try that group. I did get the issue fixed. It was a fouled plug.

 

I did have intake issues earlier. fixed that. This turns out to be a fouled plug,. Again, I'm new and learning forum practices. I apologize for not posting the code description.