My car is driving me out of my mind with the emission test. I need some
input for someone who knows a lot more than I do. Here are the details.

The car is a 95 Cavalier with a 2.2 TBI engine. It has failed 3
emission tests with high HC.

Test 1.

HC 1.9 Grams/Mile (.8 Grams/mile allowed)
Both CO and NOx passed but not by much.

My wife drove the car from a cold start for about 15 min. in slow city
traffic before the test. I figured that the engine has not fully warmed
so I drove it on the highway before next test.

Test 2 (almost passed).
HC 0.95 Grams/mile (.8 Gram/mile allowed)
CO approx. 1/2 of allowed
NOx was much lower than allowed.

Drove car for 25 min. at highway speed before test. Both test 1 and
test 2 showed spikes in the HC and CO at approximately the same points
of the test. I figured the O2 sensor may be getting weak so I replaced
the sensor.

Test 3.

This one nearly made me sick.
HC 2.5 Grams/mile !!!
CO 9.78 Grams/mile (15 allowed)
NOx 1.0 Grams/mile (2 allowed)

I drove the car to around town for an hour or so the day before the
test to let things adjust to the new sensor then drove 40 min at
highway speed right before the test.

Any ideas why replacing the O2 sensor may have taken me from almost
passing to being 3 times to high on HC? I have an appointment to take
the car in to the shop for a diagnostic test on Saturday but would like
some feedback so that I can be sure what the shop tells me is accurate.