Hi all,
another issue i discovered after years:
althrough i Always fix new sparkplugs with a torque wrench:
at mine these needs 27Nm (dunno how much lbsft that corresponds).
Anyhow it was last summer the second time I replaced my plugs on a T8 B207E engine.
I noticed two of the previous ones were slightly loose, so a fine grey vapor got out. pressumly exhaust gasses.
But this leaking also compares to a lost compression.
Now after new Sparks and correct torqueing, I found out a re-gain in power, and no more unexplainable MiL-errors.
Before winter kicked in overhere, I rechecked the Sparks for torque, and the two others were slightly loose again ???
I use Original NGK's and a good Facom torque wrench, which is good.
So I discovered when changing and re-torqueing in warmer summer times,
with colder winter temperatures, one needs to check & re-torque. The metal crimps, with bigger tolerances.
The result is less misfires, better power re-gain, less oil polution, and a re-joy of driving again.
This is the same slow process, as after a fresh brake fluid bleeding, one notices all of the sudden a better more stable braking.
The losse in power and braking force are slowly evolving, so one doesn't notice, until it really gets worse.

So I'd advice every one confronted with misfires/ sudden OBD-errors occuring: first check the Sparks & their torque before removing!
Never experienced this at other cars. Even more at Saabs one needs first to remove the coils, cover,etc...

Happy car fiddling, Harry.