Mazda Repair Questions? Ask Mechanics for Answers ASAP
Do an engine compression test you may have low compression on a few cylinders due to a possible
bad timing chain , but i'm pointing more towards a bad piston ring issue if you have to much back pressure pressure is coming out the rear valve cover vent .
Other possible issue with this is a blocked catalytic converter as you thought but you checked and cancelled out this possibility .
Check the possibility i gave and get back to me .
Like i said a cat or timing out due to t5he VVT or timing chain
A compression test will confirm this if there is a blockage you will have over pressure on some cylinders
and less on others .
Check the timing something not correct here .
How many miles on this engine ?
Like i said these engine suffer from turbo failure , i thought you checked this after i mentioned .
"Squelching noise on acceleration is sure to be the turbo, typical to have this and no malfunction codes"
Good work ..
Remove the turbo first , check the two blades are both still turning or are they blocked /sized .
And yes if nothing was getting past the turbo it will be able the breath again .
Its sized by the sounds of that on the exhaust side .
remove and replace .
The compression on #3 is low now when you have it completely removed (Turbo) do another compression test .