1994 buick park ave failed idle emission test 2.15 to high standard 1.20

seems like those may be two different issues. check for vacuum leaks and have your fuel psi checked. High fuel pressure can change your emissions numbers. I believe the fuel psi should be 30-45 psi. if its way above that then the nest step is to check the fuel pressure regulator

Any codes? any problem tune up, catalytic convener, burning oil.

Replace cat. The mechanic was correct.

the O2 sensor works on one volt .5 is around the running voltage, i would refit the air hose as it will run the converter hotter at idle.

Did you install new spark plugs? Definitely replace the O2 sensor.

This is a problem in the circuit that controls the warning light on your dash. I am not sure why you would have failed emissions for this, I would call your BMV and find out.

try have the idle mixture adjusted leaner, also it is very possible the catalytic converter is worn out, if it has over 100,000 miles it is most likely the problem. One trick I use is to change the oil before the test and get the exhaust as hot as possible jusr before the test.

High CO usualy means the O2 sensors are not reading properly. Take it to a parts store that can read codes, I know Auto Zone does in my area. If it is the O2 sensor it is an easy fix but the sensors run about $50.00 each.

have you had the the engine codes pulled and reset?
and if so what are your engine codes?
i dont know of any car that will pass emissions test with the engine light on.
we cure your trouble that caused your engine light to come on and you will pass your test.
later
paul

You might have your computer checked to make sure the circuit that controls egr valve is working.  On my vehicle, I had several egr valves changed and failed the emissions test until I had the computer changed and the PROMS updated with the latest PROM.
The EGR valve is easy to change because it is on top of the engine.  It has electrical coils that control the valve and one of the valves may be damaged where it can not compensate at idle.  If the EGR is working, when the engine first starts the engine should increase in idle speed and then switch to a lower idle speed.  This is part of the EGR system check and it adjusts as the engine increases in temperature.
There are several other reasons if one of the Emission sensors is faulty that may cause the rough idle.  The oxygen sensor, tempearture sensor, MAP sensor,...etc.  You may have a trusted mechanic attempt to read any codes on the engine.