You deffinitely need to get a code. Even if you go out and buy a cheap scan tool for $25 - $30.
I had another Toyota that had a 4 cylinder and it randomly dropped a cylinder when it warmed up. If I drove a short distance ( 5-10 miles or so or 10 minutes of running ) and turned the car off, it would have the issue when restarted. It began while sitting idling for a bit. It felt like the engine was off balance is the best I can describe it and it ran rough as hell with a bunch of lights on the dash lit. Sounded like a Subaru! Check engine, stability control and something else I cant remember that was totally unrelated to the issue.
I scanned it and it pointed to "misfire cylinder 4". I figured it was a coil and replaced the #4
cylinder coil. Problem solved!
Until the next day. The car did the same thing, Flashed the same lights. Read the same code.
I switched the #4
coil with the # 3 coil to eliminate a possible bad NEW coil. The issue did not move to #3
after clearing the codes with the scanner.
I talked to a buddy and we got our heads together and decided it had to be an injector on #4
I replaced the #4
injector and the issue never came back. It's my belief that the injector would work okay until it got some heat in it from idling or sitting after a short run without enough fuel running through it to "cool" it and because it was crapping the bed, it would "heat soak" ( my term for it ) and the injector would stick open or closed and cause the misfire. Twice I drove it with the issue short distances and really pissed off, caning the car hoping it would explode or get me to my destination and the issue would clear up with fuel flow or the injector cooling just enough not to stick.
So my guess with the little info provided is coil pack or injector.
Shops around here get about $100 to scan your car as a diagnosis over and above the repair cost. Think of the money you can save is it's something simple you can track down yourself or with the help of this forum.
Might be well worth your time to buy a cheap scanner and give it a go, even if it's to know what you may be up against with a mechanic if you decide it's not something you can repair yourself.
Keep us posted.
A funny side not on injectors:
When I asked my buddy ( a pro mechanic ) if he would get a reconditioned injector or new, he asked me a question. He asked what I was going to do with the intermittently bad injector. I said I would have to turn it in as a core. He said that should answer my my question of new or recon in this case, as they only clean, replace the seals and test low the turned in injectors briefly to see that they work and that the intermittent problem would come back and bite someone else in the a**. I bought new.