I got a check engine light and my car sounds like a dying turkey. Almost like it’s an issue with a belt. I pulled the code and it is a P0171 - “System Too Lean”

After doing a little digging on the internet, we decided to open the oil cap while it was running. The noise immediately stopped. When I put the cap back on, the noise returned.

It seems like some kind of pressure/vacuum type issue. Has anyone experienced some like this before? Any guidance on how to fix?

 

-And this is why I liked the PCV "valve" on my 1960 Healey 3000 - a rubber tube running down from a nib on the valve cover and ending next to the oil pan.

 

Rrplace the PCV breather box. I'm surprised the same info that lead you to remove the oil cap didn't also say that.