Urgent help needed to pass smog. Chk Engine light on. 96 Riviera.

Traction off light starts coming on and off. After a few times the Chk Engine light comes on and stays on. The OBD codes are:  302 (Misfire cylinder 2) and 171 (System too lean, bank 1). When I clear the codes (normally after I have changed one of the things on the list below) the lights don't usually come on right away. Normally I'll drive the car up some hills for 20 mins, run a few errands, and then the lights start coming on.
So far I've changed:
1. Spark plugs and wires (ac delco)
2. All vacuum lines
3. MAF
4. MAP
5. O2 Sensor
6. Coils
I've had the problem for two years now and smog is due again. 95% of the time the car runs great. The rpms are constant. They start to vary though when the traction light starts coming on. I find that if I give it a lot of gas they get constant again, but by that time the Chk Engine light is on and it doesn't usually go off until I clear the codes. Car runs best on the freeway, the problem usually occurs when I'm driving around town (I think the problem happens mainly in idle).
I've talked to a couple mechanics and no one can figure it out. The car is in perfect condition inside and out and I can't believe I might have to get rid of it because of this.
96 Riviera, Supercharged, Series II, 3800. 140k miles.

I am thinking fuel injectors.

I am thinking you want a big bottle of techron to put in tank per directions.

I am not thinking you need to get rid of car, but I am thinking you need to check the wiring at the ignition module and at the firewall.

other ideas?

Fuel filter possibly?

It looks like you've done everything electrical, so I'm leaning to agree with Albert about injectors. If one is clogged it will register lean and a misfire, which you are seeing.

It's worth checking the plugs and wires, especially the #2 cyl just to make sure they are good. Supercharged 3800s can be picky about wire quality. If there is a tiny flaw, you'll suffer.

actually, if there is a flawed plug wire not only will you set codes but you will kill replacement coils quickly until you get good wires on.

Thanks everyone for the tips. I ended up having to leave town for a few months but I'm back now working on the car and I've tried all your suggestions, just replaced the fuel injectors yesterday. The light is still coming on. Any other ideas?

This is a strange problem for sure. Did you change the fuel filter as someone suggested? It's inexpensive, so might as well get it out of the way.

Usually the TC/ABS lamp and SES lamps are not related, especially misfire and lean codes. But you have addressed the fueling and spark components, as well as the MAF and 02 sensors. Did you change those sensors after you started seeing problems? Or did the problems start after changing the sensors?

Still not convinced the TC/ABS lamps have anything to do with engine codes. I need to think about it some more.

Thanks Aaron and everyone. Yeah, the problems started before I changed anything. A mechanic had changed the fuel filter when I was out of town but I'm going to go ahead and change it again myself just to be sure.
I'm testing fuel pressure now with a Fuel Pressure Gauge I borrowed from O'Reillys. Getting readings of 40 in position 1 (ignition on and the engine off) and 28-30 in position 2 (idle). The needle is oscillating (not steady) for the idle reading which seems strange to me. O'Reillys says the correct reading for the vehicle is 48-55 in position 1 (ignition on/engine off) and 38-52 in position 2 (idle).
What do you think? Fuel pump?

The only way to read fuel pressure is with the engine running and the vacuum line off/plugged. It should be 50. (48-55 close enough) No other reading matters.

Thanks Derek. Yes, that scenario also gives me the 28-30 reading with the needle oscillating.

do you have low compression in cylinder 2? my dads car had low compression and that is what threw his check engine light on.