PUZZLED: TCS buzz causes Power Steering problem on 92Q/G50

[ericthered]

I've owned G50's for 15 years, and this one surprised me.

My son inherited my 92 Q now with 210K miles, and was home last weekend. The TCS on his Q is functional, but it is associated with a loudish HUMHMHMHMM repeating noise about 2 seconds long. The noise is repeatedly coming from the front right fender area (maybe low under the ABS?). Just loud enough to notice it in the passenger compartment, it sounds like a 60Hz electro-magnet, maybe a pump. Initially (a year ago) this noise occurred much less frequently or predictably, but now this Hummmbuzzz occurs maybe every 30 seconds or so when idling. We haven't located this noise exactly, so we decided to pull the fuses on the TCS in the main fuse box, and voila, the noise is gone (and so is the TCS - but it's summer in California!).

The car had a second problem that had been around for a long time. Occasionally the assist provided by the power steering would momentarily vary. Initially this problem was associated with low PS fluid and a leaking high pressure hose. After replacing both hoses the PS no longer leaks, and seemed to work fine! But as time has gone on, the PS assist has been getting spooky. Occasionally, and not predictably the steering wheel loses all feedback, like driving on black ice for a moment. Or sometimes the steering wheel seems to loose assist and "feel bumpy", just for a moment.

Now the puzzle: With the TCS fuses removed, the power steering problem has 100% vanished. I just plain don't understand it. Can anyone help me understand what is going on here?

Eric

[Q45tech]

TCS only engages rear brakes [and chokes off air entering engine].
PS computer pulses PS solenoid to raise or lower PS line pressure appropriate to vehicle speed
Trace the electrical schematic [rear of FSM] to see if commonality [fuse] between systems.

[ericthered]

Thanks Q45Tech, I never realized there was a PS computer that varied power steering boost pressure - something I never ran accross. Makes sense, one of those extras in a G50 that give it better road feel. How many cars actually go this far to create a nice variable assist feeling? Back in the early 90's I doubt it was very many.

I'll check the FSM. Then I'll need to figure out the real problem with the PS (but that will wait until next time my son travels back from school).

[goody90q45]

Are you hearing the ABS relay buzzing? It's inside the black box mounted on the ABS unit.

[ericthered]

are you hearing the ABS relay?

The noise is emitted close to the ABS pump, but I didn't really think that it was coming from there.
It also seemed near the TCS resevoir, etc., and was just the most likely suspect.
I wasn't sure what it was before because I didn't even know a PS pressure thingy ever existed, I just rounded up the usual suspects (TCS) and came to a wrong conclusion.

Now I am sad the car is 250 miles away, I can't just go over and look at it.

But I will say that the PS assist weirdness is one of the spookiest problems to encounter while driving.
It really feels like black ice - the first time I really felt it was on a hard turn at 55 MPH at night on a mountain road in winter. But it was about 38 degrees, and the car kept turning, and my stomach went ulp.
I remember it vivdly. It is one of those feelings you just can't get used to. I blamed that on my leaky PS hose and low PS fluid level at the time.

.