Question on Smog Test Results - passed but close to limits
 

This is for my 944 but I'm posting here because there are a lot of great mechanics on this board.

I took my 944 to get smogged this weekend. It passed but the guy told me that I should use 91 octane (which I already do) because my hydro-carbons were a little high.

I posted the results below but I'm wondering what I can do to improve the results and what would be the cause. The car runs nearly perfect and only has 80k miles. I am going to do a basic tuneup this weekend (i.e, cap/rotor/plugs).

http://forums.pelicanparts.com/uploa...1424116039.jpg

When was the last 02 sensor replacement? Cats can also wear out.

Wrong forum for a 944 but while you are here...

Does a 944 have a knock sensor? If it does the octane could effect how much ignition advance the engine has. (I would expect that to effect the NO levels though.)
If it doesn't have a knock sensor then it won't make a difference unless the octane is low enough to induce detonation or unless the gas is just plain crappy.

Octane doesn't do what people think it does. The higher the octane the harder it is to get the gasoline to light off. That is all. The resistance to ignition allows greater compression ratios and more ignition advance. A gallon of 87 octane and a gallon of 91 octane have exactly the same quantity of BTUs of energy.

As above: Most likely CAT and/or maybe O2 sensor.
Any sort of misfire will add hydrocarbons too...

I replaced the O2 sensor a couple of years ago but the cat is original to the car. Within the past few years, I replaced all the vacuum lines, plug wires, etc.. but I think I may have a slight vacuum leak at the air/oil separator. I'm looking for a midget to help me change those out as the space is tiny.

Regarding Octane, this car uses Chevron 91 and I can't remember ever using anything else. Yes, the 944 does have a knock sensor.

Lastly, I know this is the wrong forum but with so much great advice I have received for my 911, I trust the opinions I get here (trust but verify).