Toyota Repair: 95 corolla failed NOX, hg reading, vacuum level

Question
I failed my emission test similar to the one posted at your forum:

http://en.allexperts.com/q/Toyota-Repair-832/Emissions-NOx-corolla-92.htm

My car is running at a slightly higher temperature and I figure that might be the reason.  The temp gauge needle is slightly higher compared with all my previous cars and my 93 corolla, and the plugs are slightly whiter. I checked the Oxygen sensor reading while I am driving (wired to the cabin) and it seems fine.

I also connected a vacuum line right before the EGR valve into the cabin.  During driving at various speeds and conditions, the maximum constant vacuum level was about 3.5 inch HG and I don't remember it ever touched 5. Also, at steady speed, flat road, 15 and 25 mph, the valve did not open (no vacuum).  These are the two speeds the car was tested. In my driving the valve started to open at around 30 mph or higher. I tested the valve and found it to start to open at 2 inch HG so it seems to be right at the specification.  It also holds vacuum well. I don't find any vacuum leak around the engine. Do you think the 3.5 inch HG reading is too low and I am not getting enough EGR into the engine?  Should the EGR open at 15 and 25 mph?  I failed at both speeds.

Another thing I am trying to determine is whether the timing is off.  It's 12.5 degrees advanced with E1 and TE1 shorted, about 2.5 degrees more than the repair manual specified.  Does this small excess explain the increased temperature at all?  I wanted to retard it to see if the temperature comes down, but found out that the distributor cannot be rotated--there is one round hole in the engine and one round hole on the distributor base--there is no arc slot for rotating the distributor. In comparison the 93 corolla does have the slot for rotation. How is timing adjusted in this car?  Can I retard it at all?

I have used a few bottles of engine clearer or injector clearer before the failed re-test so I am guess carbon buildup should not be so bad as to reduce the combustion space but I am not sure.  The car has always run well and in the summer it¡¯s getting over 30 mpg.

By the way, I changed the converter before the re-test but it did not make much difference.

Thanks for taking my questions.


Answer
The timing is adjusted by the computer based on various input signals from the sensors on the engine, is there a check engine light on? If EGR flow is insufficient the check engine light should turn on. If the engine is overheating the computer would retard the timing not advance it, not sure what is causing the advanced timing readings other than that the throttle position sensor may have a problem but again the check engine light would be on.