Spark Plug Misfire

Matrix XRS used up its plugs by 90K miles - could have stretched it out another 10K, but plugs are relatively cheap and I had time to change them then. When I replaced them - the car ran perfectly well - no issues. You just have to look at the wear on the electrodes on the plugs to see if they need to be replaced or not. If the wear is severe enough - the spark plug gap will increase significantly.

Plugs usually would go before the coils - but it depends on the car. Sometimes, coils or injectors will go bad - have to properly diagnose the issue to see where the problem is. Usually pulling the plugs to read the ends is one of the first thing people do to start the diagnostic process - so you can look at them and see if they need to be replaced or not.

Depends on the car - on VW/Audi - that is probably pretty likely. On Toyota coil on plug setups - harder to say, I personally haven't seen that. On Toyotanation forums - there are a number of posters that reported weird driveability issues - some resulting in misfires or CEL being thrown. Ended up being worn plugs.

But like they say - YMMV (your mileage may vary) - as the plug wear down, the plug gap increases which requires a larger amount spark energy to "jump" that gap. Coils only supply only so much energy, if that is starting to approach its current limit - you could very well overheat/damage a coil unit. That said - I found these Toyota units pretty tolerant of larger gaps - on the Matrix - the gap opened up to little over 0.060" - which is almost 50% more than the recommended gap. Coils were still fine - car just too a little longer to start, mileage dropped a bit, but still drove OK.

Reading plugs is something that you learn over time - unfortunately, there isn't a lot of resources out there to teach you how. But there are some general things to keep in mind:

http://www.densoiridium.com/howtoreadusedplugs.php

Here is a like to some obviously worn Iridium plugs:

http://www.tundrasolutions.com/forums/engine-and-drivetrain/182063-iridium-spark-plugs/

As for the Optima redtop being overkill - depends on how you feel, what is the most important aspect of the battery (cold cranking amps, reserve capacity, vibration resistance, maintainence, mounting flexibility, etc. Myself, after running the redtop - I would have run a standard battery and pocket the difference in costs or run a lighter weight battery, like a Braille battery.

One thing to check - make sure the terminals will reach the battery posts - like in the case of the Optima redtop - some 9th gen owners found that the positive battery cable was a little tight. Some were able to use the redtop - some could not, cables couldn't reach the battery.

For your application, I would NOT recommend a Braille battery. They are fairly low CCA and designed for project cars or ones that you connect to a charger from time to time. Plus, they will require something to hold the battery - as they are significantly smaller than the OEM battery. They use screw terminals - you'd have to get a mating pair to connect them to the OEM terminals in the car.

If you are curious about them - they run between $150-$300 depending on capacity. They're claim to fame is light weight - depending on model - they run from as low as 6 lbs to as much as 15lbs. Compared to a conventional 30-40 lb battery. When I ran my Braille - I actually sat it inside the center console in the Corolla (back when I was doing auto-X) - already ran the wiring for a trunk mounted battery - so it was simple to reroute the wiring to the console box. I just mentioned Braille due to the price of the Optima battery.

As for plug gap - 0.044" is what they should be set for. Unfortunately, there is no "max" gap - as that is different from cars to cars. Some will tolerate a large gap - some will not. The max gap for your car is one where it will not misfire.

Personally - anything that opens the gap up more than 15 thousandths to 20 thousandths past spec - is too much for me. But you have to look at electrode and see how eroded it is. Not only do you have to check the gap, but you should also check for excessive erosion. Visually it will be pretty obvious - once you compare a heavily worn plug to a brand new one.

The I/M readiness monitors not being set to "ready" can be some of the toughest ones to set. Part of the issue is that even following the recommended drive cycles - readiness monitors can sometimes get stuck in one state. I/M readiness not being set will not trigger a CEL - car will still continue to run well. In fact, if you useda tailpipe sniffer - emission levels are probably perfect. But in order to pass an I/M readiness smog test, those monitors all have to set to ready.

Are you getting two readiness monitor errors or just a generic one? The downstream O2 one is set after idling for several minutes then driving under 25 mph for a couple of minutes. The catalyst on is set after running at highway speeds for a few minutes then driving under 45 mph for a couple more minutes. Also a cold soak is needed some where in there.

Also confused on the parts the dealership replaced - as those are EFI related components.

I would try a different dealership if I was in your place. As getting around the diagnostic fee - see if the original dealership will cut you a break. They did the original repair and it didn't completely fix the issue.

Used up as in worn the center and ground strap electrodes down more than I liked. As a result - gap was increased significantly. Since the electrodes were worn, it would have only gotten worse if I continued to drive on them. I could have pushed it another 10K miles or maybe another 20K miles - but plugs are cheap. Replaced them and checked/replaced the replacement plugs every 30K-60K miles or so - depending on what brand/type of plugs I used.

60K miles should be fine - everyone does this differently. Some check every 30K, some even sooner than that - all depends on how the car behaves.

As long as you don't over tighten them - there should be no issue removing and reinstalling plugs. But true - the longer service life was designed with less interaction with the plugs - you don't "have" to remove them to check on the plugs.

Most that do their own work - generally will pull the plugs at least once - just to see what the wear levels looks like and to help reduce the possibility of having plugs seized into the head, from being untouched for so long. That likelyhood is very remote though - material science has changed a bit - pretty tough to get plugs frozen into the head with corrosion or metal galling. Most that run into a problem with removing the plugs, usually is related to excessive deposits that form on the plug end. That can cause the plug to become very difficult to remove. Pulling the plugs sooner, can help reduce the amount of deposits that you'll have to turn through. If the deposits at that time are so bad, that they cause the plug to be hard to remove - that might be a good time to just replace the plugs (plugs still have lots of electrode life, but are now heavily fouled). Some may attempt to clean the plugs - but generally not recommended anymore. Example - wirebrush may remove the caked on deposits - but you'll inadvertently transfer some of the wire material to the plug. In some cases, this can cause misfires and/or provide additional sites for deposits to cling onto. Media blasters are better, but you have to make sure none of the media is left, or could damage the engine. Easiest way to approach this case - just replace the plugs. Keep and label (plug cylinder position) the old ones for a backup set and for future diagnostics.