1999 Land Rover Discovery 2 rear air suspension

Suspension problem
1999 Land Rover Discovery 2 Four Wheel Drive Manual 142000 miles

i have a problem with the vehicle wandering, especially at speed. Even in a straight line, I am constantly having to trim (adjust) the steering.

i do not think it is the steering, I think its the suspension. All of the vehicle has been checked and ok'd by its annual inspection.

the only other difference is that a previous owner removed the rear air suspension and fitted normal coil springs with a standard conversion kit

i am tempted to remove the coil springs and fit a proper conversion kit back to air suspension but berore I do, I want to know if it will make much difference