99 Honda Civic Misfiring Issue?

I have a 99 Honda Civic LX with over 200k miles. A few months ago I had new spark plugs and wires installed, and even more recently a new distributor cap. Currently the engine misfires a little on startup before it levels out and runs smoothly. After driving for a few minutes it will start to mildly misfire while idling, and worsens when I accelerate. Other times it is fine until I hit 50-55mph, at which point it strongly misfires. Revving the engine will make the misfiring stop until it downshifts. I tried some fuel injector cleaner with no luck. I'm leaning towards the igniter but would like to hear your opinions.

Sounds like a fuel mixture issue. A dirty or bad, MAP or MAF sensor and/or a bad coolant temperature sensor will be the leading culprits on why the engine misfires. Get your car scanned for codes at a real auto repair shop, this will determine where the problem really is.
Sometimes, the MAP & MAF sensors can just be dirty, and cleaning them up will get them working like new again, but a bad coolant sensor only gets replaced.
Don't just replace parts until the engine runs good again, have a mechanic get the correct diagnosis.

Check for good spark on all cylinders with a spark tester. Check compression, one or two cylinders could be low. Clean or replace the MAF sensor. Make sure the correct plugs and wires are installed. Check for fouling on the plugs. Check fuel pressure.

Hi so it has to be said what some expect from cars as old as this one is simply amazing. So designed to last 7 years or 100k miles. This one has done remarkably well. So what do you expect now a MIRACLE.

Every motor Honda makes has a common problem with the valve getting tight and the valves need to be adjusted every 60,000 miles.

Check the injectors one might not be giving enough fuel. One other thing you can do is check the compression of each cylinder to help check engine health.