Buick-Regal-engine jitter, gear reverse.

Carbon deposition, isn't it? Washing the throttle doesn't have any effect. Use two bottles of fuel, then fill them up and run at high speed. After running, see if the exhaust pipe is black. I tried it some time ago, and I feel that the car is very strong when the fuel consumption comes down. It's a little expensive to refuel the Chevron I bought in JD.COM, but it works well. I used a box (not an advertisement, personal experience, don't spray it)