Why would a 1990 buick lesabre 3800 hiccup or jerk after it reaches 55 mph?
May be fuel filter or air filter
Replace plugs and wires at the same time. An engine miss is more
noticeable when the car is in fourth gear and converter is locked
up, which is after 45mph. Carbon tracking on the plugs and wires
can cause this.
It is very common for the torque converter clutch to begin
slipping in these cars at 60-90k miles. It acts exactly like an
engine miss. It happened to my 92 Bonneville, and after looking at
all ignition items, a new torque converter fixed it. It did show a
code when read at the Pontiac dealer. Also a 92 Bonneville has
different transmission 4T60-E, it is enhanced with
electronic controls and is controlled by the computer. The
90 has a 4T60 the transitional model from the old Hydramatic
(formerly called the 440-T4 aka 4T60}. Parts are not the same in
these transmissions. My 90 4T60 has over 298,000 miles on it.