I have a 2003 V6 Sonata. Been having an issue for awhile now and cant figure it out. First started a few months ago when i started up the car and the engine was idling very rough. The car was drivable but lacked any horsepower and could feel the misfirings. I got the car to my mechanic (not the dealer) and they diagnosed an engine code back to the spark plugs and wires on the 3 and 5 cylindars (i think these are both located on the back cylindars under the manifold?) They were about to change the plugs and wires when the car all of a sudden started running good and the error code went away. They tested the plugs and wires and said all tested fine. They told me there was nothing they could do until the code reappeared. SO i took the car home and drove it for about 2 months. Only issue at this point was while idling at stop light or somewhere you could feel one cylindar miss everyso often, kind of like a small sputter. but while accelerating or driving everything seems fine (no acceleration or other issues).

Then about 3 days ago i drove the car and parked it. Got back in the car about 1 hour later and the same issue was happening again this time worse though. The car would idle real rough and then stall. I had the car towed back to the mechanic but when we got the car off the truck it started right up and was running fine. Still has the slight miss when idling though.

Anyone have any ideas? I dont think its the plugs or wires cause the problem wouldnt just go away. Could it be a computer issue or some sensor issue?

Thanks for you help in advance.

Also just saw topic about rough running when after refueling the car. My problem is not happening after a refuel. Usually been about a day or two since refueling when issue occurs.

Pull your + off your battery terminal, turn on the key for 10 sec, reconnect the batt, and see if it happens again. idk really what your specific problem is but that will clear your ECU. on a side note, have you changed the plugs and are they spaced properly?

I was having the same problem with my 2005 Sonata. I took it to the dealer and the light wasn't coming on for them so they could not tell me what was wrong. My light finally came on permenantly last week and I took it to an auto parts store and had it tested for free. It turned out to be my Camshaft Position Sensor and Crankshaft. The parts are about 170.00 and I am not sure if you can repair it yourself. For some reason I can't find a Sonata manual for my car anywhere. But at least you can have them checked and see if that is your problem.
P.S. if anybody has any info on how to replace this I would love to know.

This post has been edited by pbflorida: Aug 27 2008, 09:48 AM

Mine started to have the same sounding issue :unsure: . It only happened to me once and as soon as a turned the car off and back on it was fine. i hope i dont have to fork out 170 for parts...

took it to dealer and had it diagnosed and had the wires and plugs replaced and it seemed to help. no code about cam shaft sensor was mentioned. now the only time it stalls or rough idles is after i fill up with gas. so reading other threads i guess the next step is to replace the check valve in the charcoal evap cannister. Is changing the system purge valve easy? I am gonna check hma-service for a diagram. Looks like i might have had plugs changed for no reason.

This post has been edited by bstelmok: Oct 7 2008, 02:26 PM

Before changing anything, run a few ounces of Lucas Oil fuel additive in the tank and clean the throttle body. I say Lucas Oil because out of everything I have used in my 15 years of professionally working on cars, it seems to work the best. This did wonders for my car. Even turned off the dreaded O2 sensor light. Still gotta replace my engine mount though. These cars are nickel and dime I tell ya, lol.