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Please help! P0304 and maintenance light

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2.9K views 56 replies 6 participants last post by  Sicc562  
#1 ·
My air filter box been missing a bolt since I bought it. So years after noticing I put a bolt on the air filter box to keep it tight. Next day when I turn on the car the rpm Rev on idle on its own. So I turn car off took that bolt off and delete code. Now the rev on idle is gone. But I have a solid maintenance light. I never had any issues untill I put a screw to keep the air filter box tight. The car seems fine only u can't figure out how to remove the maintenance light.
 
#6 ·
Well, a P0304, regardless of year and model (which we now have) is a misfire in cylinder 4, which should have nothing at all to do with the other bits you've described.

And if you had it, cleared it, and it's not yet come back, it almost certainly will. But it's got to "stick" before you can really begin diagnosis in earnest (though in most cases it will be a coil going bad).
 
#8 ·
Coincidence, almost certainly.

Even a slight difference in air flow that would result from sealing a leak should not trigger a P0304.

Put that bolt in (because it should be there, the seal on the air intake box around the filter should be tight) and then proceed from there.

If you get a P0304 again, then it's time to deal with diagnostics with the air intake in the state it should be in to begin with.
 
#18 ·
@Sicc562,

You absolutely, positively need to step away from the "I have a code, let's throw parts at it," approach to maintenance. Some OBD codes are pretty directly indicative of both the area of issue as well as the fix, others, just suggestive. A misfire could be caused by a bad plug, a bad coil, wiring to the coil being compromised, etc. You gain nothing by replacing all coils, plugs, etc., "just because."

You also need to get your Owner's Manual out and read it. (Toyota Manuals and Warranties | Toyota Owners) The Maint Reqd light is discussed in detail there, and as @sdspeed has told you, it comes on to indicate an oil change is needed (if you're using the same type of oil as was prevalent when the car was made. I don't change my oil every 5K miles and haven't for a very long time, but that's the "fixed interval" at which this light comes on solid for a 2004 Solara, it blinks at startup between 4500 or maybe it's 4750 miles and 5K miles since last change, I don't recall exactly).

You are taking a disastrously wrong approach to auto maintenance that will cost you a fortune and gain you little to nothing. A strategic, analytical approach is needed.
 
#20 ·
@Sicc562,

You absolutely, positively need to step away from the "I have a code, let's throw parts at it," approach to maintenance. Some OBD codes are pretty directly indicative of both the area of issue as well as the fix, others, just suggestive. A misfire could be caused by a bad plug, a bad coil, wiring to the coil being compromised, etc. You gain nothing by replacing all coils, plugs, etc., "just because."

You also need to get your Owner's Manual out and read it. (Toyota Manuals and Warranties | Toyota Owners) The Maint Reqd light is discussed in detail there, and as @sdspeed has told you, it comes on to indicate an oil change is needed (if you're using the same type of oil as was prevalent when the car was made. I don't change my oil every 5K miles and haven't for a very long time, but that's the "fixed interval" at which this light comes on solid for a 2004 Solara, it blinks at startup between 4500 or maybe it's 4750 miles and 5K miles since last change, I don't recall exactly).

You are taking a disastrously wrong approach to auto maintenance that will cost you a fortune and gain you little to nothing. A strategic, analytical approach is needed.
I understand and really appreciate your advice. But the car is 138k mi. I purchased it at 115k mi. The previous owner was not mechanically inclined and didn't replace anything. So at this point replacing it all is probably better so I would not need to deal with that problem later. My commute to work is 65 mi a day and 65 mi back. I would rather just replace it as thoes parts have accumulated alot of miles and is probably due soon anyway.
 
#23 ·
A worn out spark plug can cause a P0304. They don't heal...it could have been a loose wire on the cylinder 4 coil. The Maintenance Required light comes on every 5000 miles reminding you to change the oil and look things over, like frayed belts or leaking hoses or leaking gaskets you can fix before oil goes all over the place. You reset the light, so look for it again in 5000 miles. How about changing the oil so you don't have to worry about that again. A set of new platinum or iridium spark plugs would be good. The rest of the things you're worrying about, put your wallet away and rest easy as long as no more check engine lights come on.
 
#27 ·
Honestly what I think is, when I put that screw on I might have put it on incorrectly causing an open gap on the air intake box. For one I only put one screw becuase I didn't realize the other one side had a missing one as well. Also I did it in the dark becuase it looked easy. The screw probably wasn't even tight. So when I started the car the next day it wasn't getting air becuase the box was probably slanted and not closed. So after I removed it and made the Box closed as it should it then went away.
 
#31 ·
In the meantime you should swap the coils on cylinder 4 and one of the other cylinders of your choosing to see if the misfire follows the coil. If it does, you have your answer as to what is failing. If it doesn't, it's then most likely either the spark plug for cylinder 4 or the wiring to the coil for cylinder 4, and a spark plug change is the next step.
 
#32 ·
Thank you. I will try that when I get home. I went ahead and order the most expensive coil and spark plug in Amazon using confirm part fitting and that seller is anazon. I hope I didn't shoot myself on the foot but. But I figured even if they don't last long like the ones In auto that's 4 times the price duralast and still aftermarket. I have 4 to replace from that single defective coil. So I won't replace all coil just that one defective one after testing like you suggest.
 
#33 ·
It's funny, but there is a parallel topic right now about a misfire on a different cylinder, but the same engine.

I am the contrarian who says that any good-quality replacement part will do, including for ignition coils. My now sold 1999 Jaguar XJ8L used Denso coils, and I was not impressed with their failure rate.

But you need to take a slow approach, and it sounds like you finally are doing so.
 
#35 ·
That paragraph underneath everything you wrote is hilarious
It's certainly not intentionally so. I have seen more heartache occur because people who show up asking for help, and having completely wrong-headed ideas, will not listen to what is being offered by individuals who have far more, and deeper, experience than they do.

If you (any you) come here seeking advice, you are not obligated to accept any of if you do not read what's offered, see if there are patterns in the advice offered, and take that into account.

Breezing into a venue like this with a preconceived notion that you want confirmed, and are going to follow-through on whether it's confirmed or refuted, is a waste of everyone's time.
 
#40 ·
Before I even say what I am about to say, I am not a moderator for ToyotaNation, nor am I trying to dictate to anyone what they can and cannot do. I am trying to raise awareness, particularly for new members, and @Sicc562 is one of those.

The default settings for ToyotaNation cause an alert to be sent to the person who wrote any given message if another member applies a "Like" to it, regardless of which style they choose. So if you like a message, the person who wrote it will receive an alert in the form of a small red dot on their avatar in the upper right side of their screen, and then they can see what kind, and on what message, by clicking on their avatar and looking in Alerts. Here is the Account Preferences page where a very long list of checkboxes for when you wish to receive notifications appears.

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While I love to be thanked (who doesn't) I always take it as an implicit thank you if the "like" on my message is a thumbs up, "love eyes," or helpful green check, and sometimes the laughing face (where appropriate).

Many are not aware that when they like someone else's message, that someone else will be notified about that unless they specifically turned that feature off.
 
#42 ·
My coils looked fine.
It's already been said that plugs or coils are the two most likely issues, with wiring to the coil being a far less likely third option.

But you are almost never going to see, literally see, anything odd looking about a coil failure. They look perfectly normal when they are perfectly dead, in most cases.