2001 Subaru Outback Bucking in Overdrive

I have a 2001 Outback with 85,000 miles. I have been having an issue with the car when it is overdrive, but at a slow speed. The car goes into overdrive around 40mph, if I am driving in overdrive say around 50 without my foot on the gas and then apply some gas it starts bucking and acting like it doesn’t have any power. If I stomp on the gas and it downshifts all is fine again. Any ideas?

Thanks a lot! Trying to get a bit educated before I go to the shop.

I’ll first apologize b/c I don’t know specifics about the Outback, but since no one else has answered yet I’ll throw out a couple of thoughts and thus give your q a bump.

First, is your Check/Service Engine light on? If so, have the codes read and post those - the actual codes, not any “words” that anyone gave you (the codes look something like P1344 or something). Many large chain auto parts stores do this for free.

Your overdrive is probably your torque converter lock up (aka torque converter clutch, or TCC). This locks the speed of the engine and transmission together to reduce engine wear and help gas mileage. 40-50mph is pretty typical for lock up if you’re under steady speed or even gradual acceleration. It should kick off (or unlock) if you stomp the throttle a bit. If the lock up is having a problem, it can sort of “stutter” - a quick locking and unlocking which would feel like bucking. At 85K this wouldn’t be odd, especially if the trans hasn’t had regular service (filter/fluid). As I said, I don’t know the Outback, but on many cars you can unplug the TCC. If you search for it a bit on the web you might figure out how to do that, unplug it and see if the problem goes away. Then you’ll know.

Of course, it is also possible that you are having an engine problem. Are there any other signs of running rough? Or is it only at around 40-50 when mildly accelerating? If there are any other signs of running rough, I’d simply start with a basic tune up (stuff like plugs, wires, air & fuel filters).

When you are “cruising” in high gear, the EGR valve will normally be open allowing a small amount of exhaust gas into the intake to suppress NOx emissions. Should you attempt to accelerate, this valve should close instantly, providing full-power acceleration. If the valve sticks open or closes slowly, it can cause a mis-fire. The repair may be as simple as removing and cleaning the EGR valve. Or you might try using the overdrive lock-out button until your average speed is 45-50 mph and maintain a slightly higher RPM and less transmission wear & tear during city driving conditions…

Thank you both for your quick response! I will try to answer some of your questions:

  1. No the check engine light is not on
  2. No it isn’t running rough, seems to be great the rest of the time
  3. I had the trans fluid flushed and new filter at 45K

To clarify a little: it only happens when cruising around 50 ish and my foot is NOT on the gas all of the time and then I try to apply some gas. At higher speeds it runs great (when I am on the gas all of the time). When it does this and I stomp on the gas it does seem to “unlock”, downshifts and then runs fine. It sounds more like the TCC then the EGR scenario listed below. Is a TCC expensive to replace or fix?
Thanks again!