Failed Emission Testing

Any chance you just changed the muffler or exhaust pipe? That can make a car fail until it is used for a while.

Exhaust system wasn't changed except for the flanges.

However, the car had been sitting for about 4 months before I drove it about 75 miles to get tested. Now I'm told that because it has sat for a while, I should fill it using Super gasoline and one of them "Garanteed to pass" engine cleaner you put in the gas.

Reading other threads, most seem to point towards either the EGR valve or the oxygen sensors. I'm hesitant to start replacing parts in the hope I replace the right part... could end up costing me a fortune if i take that route.

I even had someone suggest I put Coleman Camping Stove fuel in my gas. Apparently it burns hotter than regular gas and thus does a good job at cleaning the engine and catalytic converter. Anyone ever heard of that trick?

No, you should not be adding additives like the camping stove oil that may harm oxygen sensors. You should have driven it more before testing. Go ahead and use up the old gas and fill up from a busy station. I hope you used a "free re-test" smog center.

If you need oxygen sensors you should use the Bosch planar type. They are more resistant to contamination than the traditional thimble because of the design and they helped solve a P0420 low converter efficiency problem and avoided a new converter. The Bosch universal planar #15733 is $75 each at Kragen. *IF* you need them, there are two sensors upstream and one downstream. The universal type requires you to splice the old connector, but that's easy to do.

However, beside the oxygen sensors, you should run a bottle of Techron injector cleaner ($10 for 4 at Costco) and check the tune-up status of the car (timing belt, plugs, etc). Valve clearances are usually within specs, so if you need to check it do the front bank first, it's easier. Make sure you have new gaskets on hand and a few dabs of sensor-safe RTV to put the cover back on. An old timing belt can stretch and retard timing (increase emissions). Use a Gates timing component kit here if you need to change the T belt (over 5 yr/60K miles). If the spark plugs need replacing, I'd use NGK Iridium (IX or for $2 more the longer lasting Laser Iridium).