Hi everyone, newbie here. I just purchased a 1993 300zx non-turbo convertible 5-spd for fun. The previous owner told me it wouldn't pass CA SMOG and I am willing to mess with it myself. The car runs very well, no idling, no trouble starting, no hesitation. 94,000 miles. Everything is stock on it, no mods.

I did the following:
-oil change
-fuel additive for a whole tank of fresh gas, used up the whole tank at highway speed
-new fuel filter
-new air filter (the old ones seemed at least 5+ years old, filled with dirt and grease)
I ran the car hot for 45 min then had it tested, here are the results (Gross polluter)

HC: @15mph, measured 323 (max allowed is 59), @25mph, measured 310 (max allowed is 34)
CO: @15mph, measured 6.46 (max allowed is 0.34), @25mph, measured 5.07 (max allowed is 0.32)
NO: @15mph, measured 267 (max allowed is 484), @25mph, measured 302 (max allowed is 498)

another shop tested the car for me (free) and told me my EGR and O2 sensors are good, and his shop can't handle pre-96 cars.

Pepboys mechanic told me I needed a $2000 repair (2 new cats, 1 MAF, 2 left side O2 sensors). I have a feeling they are just shooting in the dark.

any suggestions? I have not done any diagnostic on this car myself and don't know how to go about reading the codes. Thanks in advance!

Tony