Hey all, it's been a while since I last posted on here, which means the truck has been without any serious issues...until recently.

I've got a 2000 T4R w/ 268K on the clock. A few days ago I started noticing misfire symptoms, drove it around until it threw a P0303. I took it to ToyoTechs here in Omaha and they discovered one of the spark plugs had cracked porcelain and suggested replacement so I had all 6 replaced; they were last done @ 232K miles, when I had initially bought the truck back in 2016.

Note: I had also complained about the valve covers leaking again; they were replaced a couple of years back @ 250K during a timing belt/water pump job. That issue appears to be due to bolts loosening so cleaned the area and retightened, we'll see if that'll take care of it.

Anyway, on the way back home, with the engine warmed up and at a red light, I started getting misfire symptoms again, RPM drops, etc. At highway speeds it's smooth, but from a dead stop, the truck stutters every so often and is kind of sluggish picking up speed until I reach a higher RPMs.

Since the issue is back with all 6 plugs just replaced, would it be safe to assume the eventual CEL will again be P0303? If so, what should my next steps be? I'm not well versed with troubleshooting these types of issues, never had a cracked plug before, so any help is much appreciated. I read a few previous posts regarding misfires and I'm assuming the issue could be bad fuel injector? But if so, why or how would that cause the plug to crack?

Also, on some of the misfire posts I've seen ppl mentioning checking for missing coolant? Why that question? What's that have to do with the misfire issue? This kind of worried me because when I did my oil change last fall, I had noticed the coolant in the reservoir was midway between L and H so I'm not sure if this is an indication of anything?

Thanks in advance for helping out a n00b!

Coolant drop in the reservoir may mean a bad headgasket or worst case cracked head. Is there white smoke coming out of the tail pipe? A compression test would be the best bet. Good news is it could be bad wires or coils. The cracked spark plug could have messed up the coil or the coil boot. you can swap out the #3 coil with #1 or #5 and see if the misfires jumps. Throw some ngk wires like $30.00 on amazon. If it still misfires then replace the injector.

Thanks for your response! Just to follow up, after replacing all spark plugs, the symptoms continued, although not as severe. The final solution was to replace the coil feeding the #3 spark plug. Like you had said, the bad spark plug probably caused the coil to go bad also. The truck's now running normally.