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Clunking and Bucking Buick

For the past several years, and much more lately, my 1999 Buick Regal chugs, clunks, and often bucks when I’m slowing down and attempting to stop. It doesn’t happen at high speeds, only when it’s been at 20-40mph. It seems to happen more when it’s cold, but not always. The car brakes fine, but it chugs and hesitates, and sometimes bucks. It’s got 110,000 miles on it, and this has happened on and off for several years. Advice? My mechanic can’t reproduce it and probably thinks I’m nuts.

speed sensor cam sensor weak fuel pump clogged fuel filter bad fuel pressure regulator?

I would be thinking more along the lines of the lock up torque converter in the transmission sticking on. If it feels like a standard transmission would without pushing the clutch in, then I would suspect the lock up. There is a solenoid that locks and unlocks the torque converter and they can go bad or stick. It can be tested by unplugging it and seeing if the symptoms go away. Replacement is not terrible but does require getting access to the transmission. I would go to a transmission shop and have them check it. Use an ATRA member shop though not a place like AMMCO better known as SCAMCO. In my humble experience anyway as a consumer.