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Discussion Starter · #1 ·
2006 LE 160k miles

Good day everyone. On Monday morning, while making a very sharp U-turn in front of traffic, my Siena felt like it lost most all power. Naturally, with several vehicles barreling towards me at 50 mph, I put my foot on the gas to get ahead. After doing so, it has had and almost constant misfire.

codes are P 300, then 301 to 306, which is each individual cylinder. I pulled my battery and airbox out, to check for air leaks from the starter swap I did a few months ago, but found nothing. The MAF is clean as a whistle. Battery is two years old and just fine. The wiring and coils look old and crispy, but still seem to be doing their job. The one spark plug I pulled looked fine. prior to this, I can feel a little bit of lag when I take corners, but I always chalk that up to the transmission.

I have use the search feature, even found one very promising thread, but of course the OP only said that the problem has been fixed, but didn’t bother to say why or how. Any ideas?

this post is brought to you by voice to text, so don’t get offended with any spelling or grammar errors
 

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Is there any gasoline odor when you open the hood?
 

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There are 3 possibilities... Air, fuel and spark.

Starting from step 1, you should replace the air filter and do a visual inspection of vacuum lines and make sure of things like your oil cap being closed properly. MAFs rarely fail these days, but they can get dirty, so, since you say it's clean, it's probably fine. If you have the ability to capture live data, look at your fuel trims and do the test of fogging vacuum lines and gaskets with starter fluid and watch for a change.

Fuel is a tough one to quickly diagnose. Since you get misfires on all cylinders, you probably don't have an injector problem. So, fuel pressure would be the only thing to check. Some of the parts stores have the "free" rental tools to check fuel pressures, so you might have to call around. The fact that it "lags" as you go around corners might suggest that there might be a fuel delivery issue as inertia draws the fuel away from the pump on a turn, but that's based on my interpretation of what "lags" means.

Onto spark, this can cover a LOT of items and most are hard to check and require intuition and/or parts cannon actions. "The one spark plug I pulled looked fine" Of course, this isn't the way to assess spark plug condition. You should put a feeler gauge on it to check the spark gap. If your plugs haven't been replaced, I would probably plan to do that now just because. Plugs are typically around 100-120k miles. Doing plugs will allow you to do some other maintenance at the same time which may eliminate the issue. The intake and throttle body gaskets can be replaced and you can clean the throttle body. You can also get a closer look at any potential vacuum line or evap lines which might be creating air leaks. If your timing belt hasn't been done, you're far overdue for that too.

Finally, I would also do a check to make sure you don't have something that prohibits fuel/air/spark from powering your van. Specifically, I would check for coolant in your oil (frothing/foam/butter on your dipstick) or oil in your coolant (floating in the overflow tank). If you aren't leaking coolant, you can probably stop there, but, if you think you might be, you can get a tester for exhaust gases which has a color-changing dye that changes color in the presence of exhaust gases.
 

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Just so it's been thrown into the ring for consideration:
Bad gas could also cause it. Sounds like the engine was under a sudden heavy load when making the U-turn, and likewise when the AC is on it has an added load. Of course, it would affect all the cylinders too.
 

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Discussion Starter · #8 ·
Apparently, I have gotten off easy (knock on wood). My plugs and coils came in from Amazon, so I went ahead and replaced the three easily accessible ones and the problem is now gone.
Yes, all that you mentioned above was on my list to check, including the bad gas. I did go looking for those air leaks first and didn’t find anything, so moved on to the spark.
 

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Good stuff. Honestly I cant see the coils nor plugs being the issue as it was 'all' cylinder misfires. My money would be on poor/bad fuel.
Glad it is up back running the way it should! :)
 

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Discussion Starter · #10 ·
Good stuff. Honestly I cant see the coils nor plugs being the issue as it was 'all' cylinder misfires. My money would be on poor/bad fuel.
Glad it is up back running the way it should! :)
I get what you’re thinking, but to add to the weirdness, it was still useable the entire week. If all cylinders were truly misfiring, I don’t see how it would have stayed running at all, let alone make it 8 miles to work (then back) everyday 🤷🏼

It wasn’t happy doing it and ran a bit warmer than usual, but never got above the halfway mark.
 

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I get what you’re thinking, but to add to the weirdness, it was still useable the entire week. If all cylinders were truly misfiring, I don’t see how it would have stayed running at all, let alone make it 8 miles to work (then back) everyday 🤷🏼

It wasn’t happy doing it and ran a bit warmer than usual, but never got above the halfway mark.
Again, this makes it sound like bad gas.
 

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Just a reminder that running with a misfire (flashing cel) can dump unburned fuel into the catalytic converters and melt them internally. Have seen discussions about fake Denso coils etc. from Amazon and such so I went to the junkyard when my '08 needed one and picked up a couple extras. Luckily my problem cylinder was in the front bank.
 
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