Failed Smog - Any Clue in the Numbers?

My car failed the California smog check today. I talked with three mechanics
in town about my repair options, and all three tell me I need to buy the
diagnostic package and see where we go from there.

I suppose it's to their credit that they decline to offer a firm diagnosis
on the basis of the smog numbers, but I would have more confidance in a
mechanic who could tell me the most likely cause of the failure. I have to
beleave that the emission test results themselves tell a big part of the
story. Maybe I'm off base here, but I need to make a fix-it or junk-it
descision. That descision might be easier to make before spending that first
$100.

The car is an '89 Daihatsu Charade 1.0L with 250K on it (100K since new
rings and 40K since new catalytic converter). It has new
plugs/wires/distributor cap and rotor, but no adjustments have been made
since the last smog check two years ago.

There is an unusual symptom that mey be related. Lately there has been a
problem with the idle speed dipping too low after suddenly removing load,
often leading to stalling at stop signs. This is mostly a problem on warm
days and after the engine is hot from long freeway runs. The idle speed
quickly comes back and it idles fine after that.

My emission numbers a

15 MPH Test
2068 RPM
CO2 14.2%
O2 0.6%
HC 41 PPM (147 Test Limit)
CO 0.70% (0.88 Test Limit)
NO 986 PPM (889 Test Limit)

25 MPH Test
2247 RPM
CO2 14.6%
O2 0.2%
HC 27 PPM (122 Test Limit)
CO 0.53% (0.78 Test Limit)
NO 1147 PPM (829 Test Limit)


If anyone can offer some insight into these numbers, I would appreciate
hearing. Thanks.