Always misfires? Hmmmm....
I agree...but disagree.

It uses coilpacks that tend to go bad, I think mostly due to the placement of them, they get very hot, sitting directly on top of the head. As such, since they can be had 30 each, I replaced them all after the 2nd one went bad at 80K miles.
Be sure to torque them down tight, as they can rattle loose.

No problems after that till the cat clogged.

Also, the lifespan of the spark plugs is over rated.
Every 50K miles should avoid problems there. NGK iridium for 7 each.
I run 2 steps colder since I have ASP pulley.

And, the Fuel filter must be replaced at regular intervals also, around 50K miles each or
again, you might get misfire.

MAF can also cause misfire. But mine's not that old, and it was cleaned fairly recently.

From the posts I've read, I'm thinking the front 02 sensor is cooked, partially because of age (113K miles) and also because I'm certain the clogged cat caused some very hi temps at the front, and from other posts I've seen it's the critical one used
to determine the fuel "trim". Now, I'm still trying to figure out exactly what fuel trim is, but I understand it's
sort of like a ratio, or adjustment that effects the fuel ratio. I haven't figured out how to read it, but my OBDII reader has live data, I'll have to check to see if it reads that.
Some very knowledgeable people around here.

What I am also trying to figure out is how to measure the exhaust temp before the cat, and what the specs are.
And BTW, did you ever build your ELM OBDII interface from scratch?

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2002 C230 Sport Coupe- Orion Blue
ASP Pulley-Supersprint Header-Remus Muffler-
Magnaflow Cat.
TIEN SS Coilovers-
AMG Sways, Wheels, BBK
Tinted windows and tails...