When to replace Air Surge Plenum Gaskets

[campbeam]

I have previously removed the air intake plenum when replacing the spark plugs but did not replace those plenum gaskets as they appeared to be in good condition etc.

Now 50,000 kms and a few years later, I have been trying to resolve an engine misfire and P0420 code. My 2006 Aurion now has an odometer of 258,000 kms.

After viewing a YouTube video about the P0420 error code, the recommendation was to replace these gaskets on the plastic air intake and to also check for any minor cracks. The gaskets compress over time and no longer seal resulting in vacuum leak and the error code. Actually I confirmed this when I reversed the existing plenum gaskets and temporarily got the P0430 code while the P0420 code still persisted. 

Height on the new plenum gaskets were measured at 7mm using both a micronometer and vernier calipers. Existing gaskets measured at 5.5mm except for one gasket which only measured 5mm in a section.

Following photos show the difference between the old and new gaskets when fitted.

Overall, worthwhile to replace these plenum gaskets when replacing the spark plugs.