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2007 Sonata Hesitation Issue

I have a 2007 Sonata, Automatic, 4 cylinder, 2.4 L, about 145,000.

Just recently I am getting an intermittent hesitation. Driving along around 50-60 MPH or so, steady speed, sometimes with cruise control locked in, sometimes not, it will start hesitating/bucking/surging/bogging/hiccuping (don’t know what to officially call it) a little. No check engine light, nothing weird on any gauges or tach, not throwing any codes. Speed even holds. If I hit the gas or let off the gas, it is fine. No problems accelerating or putting it into gear. Seems to do it when the engine is cold, and I haven’t noticed it once after the car has run for a while.

Took it to two shops including dealer and both either didn’t couldn’t replicate the issue, but one suggested/completed a transmission flush and new fluid but it didn’t solve the issue.

Any suggestions on what to check next or anybody have any first hand experience like this?

Thanks!

Torque converter shudder (TCS) usually occurs at lower speeds, 30-45 mph, but given the symptoms it’s still a possibility. TCS means the converter is going into and out of lock-up for some reason. Lock up is used to improve mpg at medium to high speeds, as it prevents the converter and transmission input shaft from slipping relative to the engine rotation. The solution to that can sometimes be a fluid change-out, but often involves replacing a transmission solenoid or more. On some cars it is possible to disable the lock-up function, so that’s worth a try if such a thing is possible on your car. The symptoms could also be a fuel problem; e.g. faulty fuel pump, pressure regulator, clogged injectors, or bad gasoline. You could try a bottle or two of fuel injector cleaner in the next two tanks, or that stuff that is used when there’s a little water in the gas tank, might help. If it was the ignition system it would probably throw some diagnostic codes for misfiring etc, so while that’s a possibility , less likely. For that an ignition system shop test and maybe try replacing the crank position sensor. That last part is what tells the ignition system when to create a spark relative to the position of the piston.

Yeah, I have nothing at 30-45. It happens just at 50-60 when holding speed steady, It feels like I am letting off the gas and tapping the gas until I actually do it.

Put some Iso-Heet to rule out water in the gas. So I did that, and then I bought 2 bottles of Techron Fuel Injector/system cleaner and will do that next time I fill up.

No changes in my gas mileage before putting Heet in.

You never want your CEL to come on, but I would like it throw a code at me just so I know what to go at next.

Any more suggestions or tips would be greatly appreciated.

Used to be you could just unplug something on the trans and that would stop the lockup from happening, at some MPG cost. Maybe it is still that simple on your car. That would help locate the problem. Good luck and please keep us informed.

What does anybody think of spark plugs or fuel pump/filter? Neither has ever been changed.

At 145,000 miles these things are routine maintenance that is very overdue. Why not try to figure out all these issues and get them seen to?

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I inherited this car from a family member. I am going to do both, I just wanted to see if the opinion would fix above issue.

Couldn’t hurt.