I have a 98 4Runner with 228,000 miles. It’s been having a misfire only at idle from what I can tell with no CEL. I’m changing the plugs today and then trying to go from there but I don’t know where to go from there. What steps or parts do I need to check or replace next.

 

Plugs, yes. Coils and wires as well. Then, if still present, possibly a injector. And/or valves for the misfiring cylinder. A bleed down check will tell if it's a valve. If not a valve, injector.

Hope that's some help...
Pat☺

 

Check the codes anyhow, sometimes it will store a code as a 'pending' error and not set the CEL. If there's a code for a specific cylinder, that's a nice clue.

If you haven't replaced the wires in the last decade or so, I'd do them along with the plugs and see what happens. See if there's water down in any of the sparkplug wells.

 

I presume the CEL works on startup?

 

A hint: Make sure you put a dab of silicone dielectric grease into every electrical connection. For example, a coil and the wire going over to the second plug it powers, a dab into the coil/spark plug connection, a dab in the plug where the wire over to the other plug connects to the coil, and a dab were the wire connects to the plug. 3 connections.
It's a great way to prevent the entry of dirt, oil, crud, etc that's so prevalent in the engine compartment. Good for every electrical connection. If you open a connection, a dab before you close it up again is a good policy. It takes a while to get into the habit, but it's a real good habit to have. Get yourself a good size tube of the stuff. You'll use it up faster than you think.

It's also good for things like rubber o-rings, etc. All rubber tubes and so on. Keeps the rubber from drying out, and sticking to whatever it's connected to. Helps o-rings last much longer, and aids them in sealing up whatever they're in. Just a thin wipe of grease on the o-ring before you install it. Also, it helps keep rubber door and window seals from freezing to the body during cold winter temps.

Just a thought...
Pat☺