Lexus Power Steering Problem

We have a 1990 Lexus LS400 (original owners), and we recently had the steering system rebuilt with: A1Cardone pump, new PS rack, new high and low pressure hoses, and had both (rack and pump) solenoid screens cleaned. We are on our second PS pump, thinking the first one was defective (same brand). We STILL have a shudder in the steering when making a sharp turn at very low speed. It’s as if there’s not enough pressure at low RPM’s to move the rack freely. When we straighten out the wheel or accelerate, the shuddering goes away and all is perfectly normal. What is the problem?

Is the drive belt to the pump slipping? When you turn the wheels sharply, the pump needs maximum power transfer from the belt. If it slips, the pump will lose power and cause a shutter. I’d recheck the tension and/or replace the belt.

Thank you so much. I’ll have this checked ASAP-we are very frustrated at this point! Very good suggestion and I hadn’t thought of this (seems like the mechanic would have!).

I just had someone check the belt, and he said that the idler pulley keeps the tension on the belt, so that may not be the problem. I question him as a mechanic, though, but no one is around who’s really qualified on a Saturday. Is there any validity to what he’s saying? Also, when you are at a standstill and turn the wheel, it makes a sound like a saw (not very loud, but constant until you take the pressure off).