Keep in mind the road and wind conditions.

Test the vehicle in both directions on a flat road.

The front wheels are not in alignment.

Adjust the alignment to the specifications. Refer to Wheel Alignment Measurement in Wheel Alignment.

The steering gear valve is not in balance.

With this cause, the steering effort is very light in the direction of the lead and is heavy in the opposite direction.

Replace the gear valve. Refer to Power Steering Pump Flow Control Valve Replacement - Off Vehicle .

The steering shaft rubs the inside diameter of the shaft tube.

Align the column.

The tires are worn.

Replace the tires. Refer to Tire Mounting and Dismounting in Wheels and Tires.

The tire pressure is low.

Adjust the tire pressure. Refer to Tire Inflation Pressure Specifications in Maintenance and Lubrication.