Power Steering Problem

[StuP]

For the last few months the power steering on my IS200 has been what can only be described as lumpy (heavy then light then heavy) when the weather and engine has been cold. It is ok at higher revs when driving but at relatively low revs after just starting (pulling away) the problem rears its ugly head. Anyone got any ideas or experienced the problem before? I've changed the fluid but no difference

[iano21]

just checking but did you use a right light oil for the power steering as a heavy oil could cause that? cause if the oil was heavy it will still thin out when hot and work fine. .

after that sorry to say but id be looking at the power steering pump!