I have a question about the power steering on a '90 LS400 with 91k miles. I recently noticed that the power steering stiffens up when making turns at low speeds. The problem went away temporarily when the fluid was topped off. I was first told that I had to replace the rack & pinion. Do you agree?
I had replaced the P/S pump in the past due to a leak. Presently there are no visible fluid spots in the driveway/garage, and I rarely have to add fluid to the reservoir. Does that rule out the possibility of a leak? I read one of your articles about a power steering solenoid being clogged. Do you think this may be my scenario?
If steering was difficult in both directions while the power steering fluid level was low, and filling the fluid reservoir to the proper level cured the problem, then let's find the leak. No drops of fluid visible down below can mean one of three things -- either it's a very small leak, the steering rack seal(s) are leaking, or the fluid is being drawn into the engine by a defective Air Control Valve.
Steering rack seals prevent the pressurized power steering fluid from escaping out the left or right side of the steering gear. The seals are protected from dirt and grime by accordion shaped expandable plastic covers called "dust boots" -- like on the front forks of a dirt bike. When the oil seals leak, the fluid fills up the dust boots as opposed to dripping down to the pavement. This can be determined by removing the dust boot retaining clamps and pulling back on the boots. If fluid comes gushing out, there's your answer, replace the seals or the entire steering gear.
The Air Control Valve is mounted to the power steering pump. By controlling vacuum in and out, the valve signals the powertrain control system to raise idle speed when power steering pressure is high -- to prevent a stall. This switch can leak internally; causing PS fluid will be drawn out of the pump by engine vacuum and burned up in the combustion chamber.
If it it's not that simple, and the problem does occur while the power steering fluid reservoir is full, then it could be an issue with the pressure solenoid. But it's going to require testing by a technician with a power steering pressure gauge to first eliminate the pump, gear, hoses, etc. as possible causes.