About a month ago, I had the PO420 code and put in a new ignition coil, the code went away for like three weeks, I was so happy I thought it was fixed.
Then yesterday, after a long drive, it mysteriously reappeared.
My mechanic said the plugs are ok, I have new coil in there, and the EGR valve was cleaned out.
Prior to cleaning the EGR valve and replacing the ignition coil, its acceleration was misfiring under a load , but after the egr valve cleaning and new coil installation; it accelerates smoothly under all circumstances.
What should I check now? CAT? TPS?
The car has to pass emission in October, I may buy one of those 02 sensors that erase this code.
Its a 2000 protege 1.6L engine, car has 221 200 kilometres .
I dont like throwing parts at a car!