QuestionI am seeking advise, My wife's 2005 Hyundai Sonata started acting up today. It seems that when it shifts into 4th gear and reach a cruising speed of about 45 to 55 mph the rpm needle starts to fluctuate. it drops about 500 rpms the regains to normal position. this happens with steady pressure to the gas pedal. this happens every 5 to 10 seconds. based on my experience I am going to give the car new plugs wires and fuel filter, but anything beyond that i am not sure. any help would be greatly appreciated thank you.
AnswerBased on your description, it sounds like the torque converter clutch is either slipping or turning off and on.
Torque converter clutch operation is in part based on the readings from the throttle position sensor, so it's possible this is defective.
It's also possible the problem is within the transmission, either in the torque converter or in a transmission component that could cause insufficient fluid pressure to reach the torque converter clutch.
Check your transmission fluid level. If low, fill with SP-III fluid and check for leaks.
Check for diagnostic trouble codes in both the engine control module (ECM) and transmission control module (TCM). There may be a code stored that will point us in the correct direction.
If you have no trouble codes and the fluid level is proper, you'll probably need to take the car to a shop well-respected in driveability and transmission diagnosis to determine the cause. A good diagnosis will require a scan tool to be able to monitor data from the ECM and TCM to determine whether there is a problem with the torque converter clutch or whether it is being commanded on and off due to faulty input to the TCM.
