If it's a 165, your problem is most likely in the control valve linkage and/or adjustment. The whole package is behind the grill, in front of the radiator. The pins and links that operate the valve spool become worn over time and adjustment becomes necessary. Wear and excessive play in the shafts and bushings throughout the system are also a factor, Often these bushings haven't seen grease in years. As a rule, I would check the valve linkage with the engine off first. Open the grill and dust off the linkage enough to see what's going on. Then grab the draglink and try to force it by hand in both directions. There should be enough freeplay to move the control valve linkage enough to see movement of the valve spool in both directions. The valve is spring loaded to neutral and should remain there until some effort is applied to move it one way or the other. In your case, I suspect something is either out of place or out of adjustment causing the valve to be somewhere other than neutral when the steering is at rest.That causes the steering to take off on it's own when you start the engine.