2001 Impala w/ 175K+ miles on it. Has run really well 'til this summer, when it really lost any sort of power when asked to accelerate (passing, merging at highway speeds, up hills, etc.). This came with a check-engine light.
Took it to our trusted mechanic, who diagnosed a clogged catalytic converter. He installed a 3rd-party CC (for half the cost of an OEM part) with the caveat that sometimes the computer sensor “knows” when an OEM part hasn’t been installed and it may throw another check engine light at us.
Which it did. The loss of power issue was fixed?it now has all the guts it ever did, thankfully. But now it has a different problem of lurching while driving. This can happen at city or highway speeds, with or without cruise engaged. You can hear the engine’s rev speed changing as the car lurches. Easing off the accelerator (or hitting “coast” on the cruise control) will make it stop, but sometimes only for a second or two. It comes and goes and is probably present for maybe 2-4% of total drive time, so it’s more an annoyance than anything.
We took it back to the mechanic who ran the requisite diagnostics and came back with nothing new, but thought it could be related to the 3rd party CC. He installed an OEM converter, but it still does the same lurching thing.
We can’t relate it to any brand of gas, any temperature, any speed. Totally random.
Any ideas?
Thanks
-ArtGekko
Do you think it’s possible what you’re felling is the torque converter clutch disengaging and re-engaging?
Tester
Honestly, I wouldn’t have a clue. I’m mechanically challenged! 
Why would the torque converter clutch do that? And wouldn’t it exhibit other symptoms like reduced fuel economy or power?
-AG