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My 04 sonata with 100,000 mi had a misfire in cylinder 5 code recently. I replaced the plugs and wires and the misfire went away. It drives fine the majority of the time but once in a while the engine will rev between 3000 and 4000 before shifting. I notice it the most when accelerating around 40 mph. Not sure how changing the plugs and wires could affect the transmission shifting. Any help would be appreciated.
 

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Have you ever checked or changed the trany oil ? If the oil is very dark I would change the oil. I just changed mine last week at 150,000 km. It was a very dark color.I bought the car with 85000 km and the oil looked ok. Car trany is just fine before and after the oil change. In severe driving conditions you may need to change the oil more often. I just opened the trany drain plug and measured 4 liters waste had come out. I poured 4 liters of Sonota compatable sp3 oil back in. I used Lucus semi syntheic oil. No screen or filter to change. Reading I learned there is a filter that usually won't require changing...you just never know? That filter is a days work I'm told so I did not bother with it. That is my experiance and I hope it helps.
 

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Engine and Trans program updates a number of year back, maybe related to old programs..

Install last versions as offered on GDS and go from there.
 

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I have previously changed it around 60,000. It is due for another change but the slip wasn't occurring prior to me changing the wire and plugs and the slip is sporadic, so I don't feel like that is the problem. I read somewhere there is a TSB No.(04-40-006-2) for a PCM reflash but I would need to bring it to a dealer for that. Would rather fix it myself if possible. I also read the speed sensor's can go bad, but I'm almost positive that would give me a check engine code which I don't have at the moment. Thanks for the feedback.
 

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Need to start with fault code search of PCM and TCM to see if either module determined if any input/output circuits seen to be at fault..

proceed from there.. I would assume you have fresh load of ATF in transmission is freash, so should slow down solenoid drag due to varnish.. verify all main ground clean also to reduce/eliminate any chance of excessive voltage drop.
 

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thats a very common problem with our sonatas. frequently there are two sensors to blame. in my case it required that i change them and have hyundai perform a software update to fix the issue. the sensors are called the input speed sensor, and output speed sensor. i would recommend a technician install these and have hyundai perform the update.


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