Mazda Repair: 1995 Mazda Millenium, engine oil pressure, psi readings

Question
Good morning, I've had my Mazda tuned, an oil change, and have replace the timing belt and replaced the struts it run great with the exception of when I'm idle at a stop light the oil light indicator slightly blink on and off. I've taken it back to my mechanic and he slightly advance the carberator idle above the specification. it appear to correct the problem, but its back too doing the same thing I've check my oil dip stick and its show the oil level at the correct level can you advise thanks. Second question this car has 4 catalytic converter two in the rear of the car and two under the manifold in the front I've replaced the rear but just found out from my mechanic about the front two at a whooping $700 plus each parts only! (to pass epa emission it pass this year barely but my mechanic said they'll have to be replace)is their a cheaper way or cheaper re-manufacture parts you can suggest. thanks

Answer
The light is telling you the oil pressure is low.  You can have a full crankcase of oil but if the pump cannot maintain a minimum pressure the light will come on.  Ask your mechanic if he can preform an engine oil pressure test to obtain it's actual PSI readings.  The minimum should be 20 with an optimum of 30+ at idle.  At RPM the pressure can increase to 90 PSI.  

Low oil pressure at idle can be a sign of internal wear, it could also be a pressure sensor failing which may give the cars computer incorrect information.  Oil pressure can be increased by using a heavier grade oil (10w40 or 20w-50, ask your mechanic it depends where you are as to what you can use) and switching to an oil filter brand that uses a reverse flow check valve (a Mazda brand is best) this check valve does not allow oil to flow back to the pan once it passes the filter.

Do you have the 2.3 Miller Cycle or the 2.5 engine?

On the converter issue sadly the Millennia was a short lived concept.  No after market was ever developed to support the car.  Mazda is the best and sadly only source for parts on this machine.  If you want direct replacements that can go the distance stay Mazda, pay Mazda, otherwise you should be able to find am exhaust shop that may be able to offer a welded in universal type converter system that will do the job though with a lessor quality.

On well driven cars the primary converters fail first (front) the secondary converters fail more on cars that make short hops.  The converters do not get to high enough temperatures to burn off corrosive elements, by products of combustion and so they rot out.