So I've had this for years on my car . It's a slight misfire between 800 and 1800 RPMs. There are no codes reported, but I know it's there. It seems that the problem gotten worse when I installed spark plugs with lower Gap since I need that pushing more power.
the biggest suspect is ignition coils, car has nearly 94,000 miles and I know they are still original. Anyone ever replace the ignition coils to resolve this issue and what brand did you use?
I replaced coils on my e55 Mercedes about 6 years ago I bought cheap no brand ignition coils which were one-third the price and they have been running excellent with no issues since. So I'm thinking maybe brand isn't so important on ignition coils since it's a simple device?

 

Coils matter a lot. Do not use cheap ones - see existing threads.

It can't flag codes unless it has fairly consistent behaviour.

If you have OE coils, plugs, no changes to other items (avoid K&N, proper fuel, stick to maintenance schedules or better, make sure OBD monitors all set, good battery fully charged, etc), all tends to be OK.

You can get a coil tester.

You can stress them fairly well at say 50mph uphill.