No. The NOx (oxides of nitrogen) are only created when the combustion in the combustion chamber gets over 2,500 degrees F. Completely normal. You have to remember that combustion is literally a small contained explosion. Damn thing is gonna be hot lol. Somewhere along the line your vacuum system is not drawing the oxides back into the chambers to burn off. Check your vacuum lines and diagrams first and see if the vacuum is the culprit. Even a small hole can have major consequences especially if it's in a low pressure line. Whatever air may have been going through it is now equalized by the pressure outside the hole. Let me see if I can get a diagram of the vac lines for you.