Having recently purchased a IS350C, I've noticed that the steering is somewhat stiff. After reading information on this forum about the Steering ECU Module. If I change the Steering ECU Module, to one from a IS250, will the steering be lighter? I bought this car for the convertible hardtop, not concerned about the handling. Thanks

 

Howdy and welcome to CL... it would best to pull the battery and look at the PN of the unit installed. It should be 89650-53100 or 53120 which are exclusive to the convertible.
If it has F-Sport 2011-2013 EPS ECU PN: 89650-53082 it's fairly light and drives way better than base model. What I found was the more aggressive you drive it, it gets lighter and lighter. A battery disconnect will reset it making it firmer. Does it show signs of a new battery in place?

The IS-F ECU is indeed firmer especiallyif ECT mode is enabled. PN: 89650-53041 or 53042

#EPS ECU

 

The battery was replace when I bought the car. I will try the aggressive driving. Thanks

 

Another is maybe the previous owner installed the RC/GS-F LCAB. Under the car you can poke them, and they will be squishy if OEM. Possibly maybe the +20 offset for extra caster make them slightly stiffer as well?

With the RC/GS-F bushing the durometer will be stiffer. This adds some weight feel to the steering wheel.

 

do you know if the is-f steering ecu is firmer even on the normal, non-ect mode setting? Compared to regular IS or f-sport?


do you know if the is-f steering ecu gets lighter and lighter the more you drive it like the f-sports ecu?

 

Having worked in a frame and alignment shop for years, the tiny caster change would not be noticed by anyone installing +20 offsets. Cars like ours with 8° of caster will feel very heavy if for example on a slope or bank at low speed, you will feel noticeable pressure being applied to keep the car from the low side ditch. I.e. keeping it between the lines. As for bushing durometer, this helps response, feel, firmness but wouldn't increase effort while rolling. JM2C



My car is the last gen F-Sport (2013) and came with the 53082 EPS F-Sport ECU and currently has the 53041 IS-F ecu. Yes, IS-F ecu is firmer all the time but it also gets lighter over time like the F-Sport ecu. After moving and my commute being reduced it sits more, and after three weeks of being off, it and the engine reset as computers shutdown to conserve energy.

 

Just wondering, if the slight increase in caster makes a negligible difference in steering effort, what or which alignment adjustments would effect it?

also, slightly off topic but if the steering wheel is not centered but happens to be let’s say pointing at 11 o clock but yet the car is driving straight, does this mean the left wheel has toe in or something? And would it only/mainly be adjustments of the tie rod ends (inner or outer?) to remedy this?

 

For clarification, caster is the for aft spacing of the upper ball joint compared to the lower ball joint. Like a motorcycle fork (+ caster) or shopping cart (- caster).
Anyway, caster induces highest steering wheel input followed by camber. However in our case electronics can also be a huge factor.

Back in the day I used to modify hydraulic PS by replacing the torsion bar with a stiffer one to increase steering wheel input effort. In short, the steering wheel applies rotation to a valve that feeds oil to a piston for assist. The valve and torsion bar control oil flow rate to the piston and with some parts swap you could take a car that steered lock to lock with a broken pinky finger and make it take two hands and some effort if thats what the owner wanted.

As for the wheel position, first you look at totsl toe. If total toe is zero, adjust both tie rods equal amounts the opposite direction to straighten the wheel.

Few here will sign up for this but I set the toe based on tire wear not some number from machine. I also, straightened my own steering wheel... PS if your tire wear is good, loosen the lock nuts boot clamp and turn each tie rod the same amount the same direction. One is left and one is righthand thread.