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ase_master327, Shop Owner
Category: Car
Satisfied Customers: 5288
Experience:  +15 years experience on imports and domestics. Bumper to bumper diagnosis & repair.
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My 2004 Hyundai Sonata has began to randomly set an engine

Resolved Question:

My 2004 Hyundai Sonata has began to randomly set an engine check light, run rough(due to misfires) for 5 to tem minutes, and then returns to running normally. The check light eventually drops off in a couple days, and then the process happens all over again in any number of days after that. I had a tune-up done, and even the timing belt. Sometimes the light will go on and it doesn't even appear to run rough. The garage I took it too said all of the codes were from misfires, and they could not get it to fail. It happens randomly. What can this be? Thanks, XXXXX XXXXX IL
Submitted: 8 years ago.
Category: Car
Expert:  ase_master327 replied 8 years ago.
Hello, and thank you for choosing Just Answer!

You got the 4 or 6 cylinder engine in your Sonata?
Customer: replied 8 years ago.
Expert:  ase_master327 replied 8 years ago.
OK.. sorry it took a few minutes to get back with you.. I had a few phone calls.

Anyways... Which ever cylinders it said were misfiring, I would look into the ignition system on those cylinders.. make sure everything is hooked up and connections are clean and tight.. all that good stuff.

If you don't find anything by 'tugging wires'.. then I recommend looking into the general state of tune of the ignition system, and possibly even the ignition coil pack.

Here is what I have on testing the coil pack.. but with the way the problem comes and goes... I almost HAVE to say, there is a loose connection somewhere.. You may even be having a prpoblem with a bad engine mount, letting the engine twist, and it is actually pulling some connectors loose. So you will want to look into that also. Engine mounts are pretty easy to check.. just set the parking brake, and oput the transmission in forward and reverse gears.. and rev the engine just a little bit.. to see the engine move.. You are looking for more movement in one gear than the other.. If it does, then you have a bad engine mount.

Otherwise, here is how to test the coil pack:
Customer: replied 8 years ago.

Really....that's your answer?


How about some insight in to possible causes???

Expert:  ase_master327 replied 8 years ago.
OK.. since you put it like that.......

I am going to opt out, and you can see if someone else will come along to help you make sense of this problem

Have a nice day, and thank you for choosing Just Answer.
Customer: replied 8 years ago.


I didn't scroll far enough down. You "If it ain't broke, don't fix it" is all I saw.

Thanks for your ideas.

Expert:  ase_master327 replied 8 years ago.

It happens..
I thought it seemed like you didn't even read all of that stuff I typed in and uploaded for you.

That 'If it ain't broke, don't fix it' is my 'motto'.


If I have been helpful, click the Accept button. If you still need help, just click the Reply button. The information is not free for me.

Customer: replied 8 years ago.

All of the cylinders misfire when this happens. The light has gone on when I am driving along, when I am stopped waiting for a red light, and when the car is in park warming up before I go. I tend to get a lot of corossion on one of my battery connectors. Could this, and older battery, or bad battery cable or connection also cause this? I seems like it just forgets where it is at for a few minutes, remembers, and then gets back to business. I was wondering if the computer could cause this also?

Expert:  ase_master327 replied 8 years ago.
Loose connections corrode.
Corrosion eats the wires.

Yes, the corosion could cause it. I have looked for any TSB's on the problem, and cannot find any.. so you just might be on to something there.

If the wires are loose and corroding on I said in my first post, it will mess with signals to and from the computer.

To go into much more detail, though.. I need to know the exact codes it gave you. If there are misfire codes, then you can almost guarantee there are other codes associated with them. Misfire code only says the cylinder is not working..... You should have rich or lean codes, which will give some sort of direction to go in.

With the corrosion on the cables.. I almost have to say... again... the problem is in the ignition system. Loose, dirty connections will definately cause problems like this, and eventually start burning up parts, because the electricity hads a hard time getting past the corrosion. Low voltage makes the components work harder thatn they have to, and heats them up.. that is what burns things up... but it doesn't seem like anything is burned up... YET.... So you are on the right track.
Customer: replied 8 years ago.

I will see if I can get codes off of it tonight.

Expert:  ase_master327 replied 8 years ago.
Let me know what you find.
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