A small vacuum leak at idle can cause a fuel system lean fault but not necessarily cause high tailpipe emission output. The PCM uses adaptive fuel trim to correct the air/fuel ratio, when the fuel trim correction reaches 25% a fault is recorded.
Just when it’s convenient! No, but seriously, that question makes its seem like I knew about the process you are discussing which I (super obviously) did not. Can you give me any indication of where/how/how much? I’d pay $100 to figure out whether it’s a true polluter or not. (A part of this is my fault, asking whether such a test exists really should have been my first question.)
4 Gas Analyzer Call around and ask if any shops in your area still have one or who might…
Start here; Locations, FAQ’s and more, way more…
Costs up to $25 (per the FAQ)
It seems like there must be a gadget available somewhere that performs that function that is diy’er priced. It might not measure every gas (maybe HC only for example) and wouldn’t be as accurate in an absolute way as a pro shop version; but a version that is relatively accurate would be very useful to a diy’er. In other words, it might not provide the exact HC reading, but you could use it to compare the HC readings from one of your cars to another one, and comparing how tailpipe HC is affected on a single car, say with one type of oil to another, one version of a replacement part to another, etc.
It seems like the technology for making an HC gas measurement is pretty similar to an alcohol gas measurement, and gadgets for measuring alcohol on the breath are used routinely to check for drunk driving.
For my final comment, if you are that concerned, scrap the car and get a newer model. And sleep well.