Toyota Repair: 93 Toyota Corolla - Failed CA SMOG Test, combustion temperatures, combustion chambers

Question
How does one remove carbon build-up. Is there an off the shelf product that can be added to fuel or injected into air intake? Any recommendations here?
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Followup To

Question -
Ted,
This is '93 Toyota Corolla 1.8 L, 140Kmi. (in the form of a geo prizm). Well maintained engine with all the usual plugs, wires, dist, etc.
Today failed CA smog after several years of passing OK. This is NOT a CA equipt car (its federal/canada) (the book only mentions EGR for Ca cars).  Do I even have EGR?  or is it there but just not controlled.
Runs wonderful, no codes, no check engine light.  Unfortunately I don't have previous test result to compare.

@15mph, 1905 rpm;
CO2% = 15.0, O2 %=0.0;
HC(PPM) Max=92, AVE=21, MEAS=2;
CO% MAX=0.55, AVE=0.06, MEAS=0.02;
NO(PPM) MAX=716, AVE=150, MEAS=772;
Result = FAIL

@25mph, 2362 rpm;
CO2%=14.9, O2%=0.0;
HC(PPM) MAX=57, AVE=13,MEAS=0;
CO% MAX=0.54, AVE=0.05, MEAS=0.01;
NO(PPM) MAX=764, AVE=136, MEAS=926;
Result =FAIL
Anything I can do to get this back on the road for a couple more years?

Thanks,
Dave



Answer -
Only CA certified corollas had the egr system, federal and canada did not require an egr system.
The reason for the higher than the maximum readings for NOX are normally caused by higher than normal combustion chamber temperatures, the HC and CO readings are very good this means that the engine is mechanically sound and fuel efficient.
NOX gases are directly related to combustion temperatures so look for a cause for this, the engine may be running hotter than normal, timing also has an effect, make sure the timing is set correctly, try changing the thermostat with one that opens at a lower temperature (180 degrees), check the cooling fan to make sure it comes on when the engine warms up. Another reason may be that there is a lot of carbon build up in the combustion chambers which will raise the compression ratio causing higher temperatures.

Answer
The correct way is to remove the cylinder head and clean the carbon with a wire brush attached to a drill of some sort either electric or air powered.
There are some chemical carbon removing methods where a chemical mixture is introduced through the fuel injectors or the intake system, I have also heard of mechanics that introduce ATF or water into the intake with the engine running at high rpm, this will break the carbon loose but it has to be done by someone that knows what they are doing to prevent engine damage.
Check with some of the local repair shops to see if they have a method that works and are willing to do it without removing the cylinder head.