Can a new 12V reading high, cause Ignition Coil to misfire?

Most likely you have a head gasket needing repair/replacement. Major work...sorry. Battery reading 14.7 is normal and would not cause a problem.

 

You didn't read up on these beforehand yeah you're heading for all kinds of fun I envy you not

 

That reading is the inverter charging the battery

 

If the car is off, a new agm battery should measure close to 13v
I’m wondering about your meter

 

If you're checking the car's battery while in ready mode you will see about 14.5 volts now turn the car off Wait 20 minutes take another measurement it'll be around 12:00 If it's under 12 that's problematic You need 12 volts in the 12 volt system not 11.9 or any of that

 

A reading like 14.2 when the car isn't READY is kind of a mystery. Like bisco, I'm wondering about your meter.

But anyway, I doubt that mystery is behind the misfiring—after all, the system voltage is around 14.7 a lot of the time when the car is READY, and the ignition coils work fine then.

Inconveniently, misfiring can have a lot of causes and checking them all can be hard. The P030x codes you have are not specific to the ignition coils; those codes only tell you misfiring is happening, nothing about why it is happening. (If you had P035x codes, which are specific to ignition coils, that would be a different story.)

There's kind of a helpful article on misfire diagnosis in the Second Quarter 2009 issue of Toyota Tech (starting on page 15).

There will be a chorus wanting to jump right to "blown head gasket" as if nothing else ever causes misfiring, but lots of things cause misfiring. So at your mileage, you might want to do some of the tests earlier rather than later that can rule a head gasket leak in or out, but still not assume the worst until a test shows it.

 

The article is from a 2009 issue of Toyota Tech, which is from when the gen 3 (model year 2010) came out.

That article tells you about some of the gen 3 ECM features that can help you diagnose a misfire. It kind of assumes you picked up gasoline-engine basics somewhere and know the basic things (fuel, compression, spark) that need to be checked and how.

The head-gasket chorus would want you not to spend too much time looking for other causes, in case it is the gasket and there could be risk of further damage. So where you might, with a younger engine, start with the easier tests like fuel and spark and leave compression testing for later if you don't find an easier problem, at your current mileage you might move compression testing toward the front, as that's one of the ways to detect a gasket leak.

Many here have suggested the best test for the gasket leak is to pressurize the cooling system and use a side-camera borescope through the spark-plug holes to see if any drips of coolant form in the cylinders at the junction with the head.

 

Pull the spark plugs out Make note of which cylinder they go in and as you pull one out look at it with a small magnifying glass You're looking for micro water droplets and you probably will see some Note the cylinders that they are in Note the other ones are dry probably where your misfire is beginning or such.