# rpm fluctuation when turning steering wheel



## coolsig (Jan 4, 2011)

My rpm drops down when I start the car and turn the steering wheel to the left or right. This just started happening a couple of weeks ago. Initially I thought it was a glitch that would pass away the next time I started my car but no. It happens almost consistently. Any idea whats causing this ?

Thanks
Noel.


----------



## PanEuropean (Nov 3, 2001)

Josh - this sounds like a question for you, it's a bit out of my field of expertise. 

Michael


----------



## PowerDubs (Jul 22, 2001)

When you turn the wheel, load on the PS pump can cause a drop in RPM which can also cause a drop in output on the ALT. Since the car is wanting to maintain both idle RPM and voltage, it will fluctuate and try to adjust.

You can try this in just about any car in a driveway or parking lot while watching the tach move. Modern cars handle it better than the old cars (especially old carburetor fueled cars). If you saw the wheel fast enough back and forth, I've even been able to stall an old car simply with the steering wheel.


As to why you say it is just happening recently..no idea. I've never tried it on my Phaetons. Maybe you just noticed it? Or.. check your PS fluid level.


----------



## IwasHuman (Jun 30, 2012)

I notice this on my P as well, always have. I've also noticed it on every car I've ever had. The RPM's will drop while your turning the wheel, but once you release it, they should steady themselves again. Usually if you're forcing the wheel over against it's full lock stop, the rpm's might drop a bit more. I know our Volvo does that a lot, because we spend a decent amount of time in full lock trying to turn that bus around parking lots.

To testify to what Josh said about carbureted cars, in my old FSJ I idled around 550rpm. On cold mornings I'd watch the rpm's dip down to 250-300, almost stalling the engine when turning while standing still. 

It's probably normal and just never caught your eye, but if you're 100% positive it's never done this before, just keep an ear out for PS pump whine. I've seen cars that will struggle more so to keep the engine rpm's up when the pump bearings start failing. Have someone turn the wheel while you stand outside and listen for a distinct whining noise. If you hear it, and it should be pretty noticeable, first check your fluid level and if all is fine, get a trained set of eyes/ears on it. 

Aaron


----------



## PowerDubs (Jul 22, 2001)

IwasHuman said:


> we spend a decent amount of time in full lock trying to turn that bus around parking lots.






Surprised to hear you call the Volvo a bus, when the Phaeton is almost 2 feet longer.


----------



## StevenFT (Jan 26, 2012)

PowerDubs said:


> Surprised to hear you call the Volvo a bus, when the Phaeton is almost 2 feet longer.


Volvo "R" cars have an embarrassingly wide turning circle. I believe it's due primarily to the size of the front brakes in relation to other components in the front end. My Phaeton will make turns that would have required reversing in my old S60-R.

Steven


----------



## IwasHuman (Jun 30, 2012)

Until you drive one, you have no idea, haha. The best numbers I could find"

S60 FWD/AWD 106.9" wheelbase 19.5' radius 39.0' full circle (U-turn)
S60R AWD 106.9" wheelbase 21.3' radius 42.6' full circle
Phaeton 118.1" wheelbase 19.6' radius 39.3' full circle 

It doesn't seem like much of a difference, but it's huge. To the point that my wife, who's timid of larger cars, is more comfortable parking the Phaeton at the stores than her Volvo. 

I'm not quite sure that the brakes have much to do with it though. The geometry in that chassis for turning radius is bad, even with the non-'R' just because they have a pretty decent sized 5cyl up front, and this big AWD transaxle. The engine bay is massively wide leaving not much room before the tires will rub. Most of the suspension components are the same or very similar in the 'R' and non-'R' model, but the steering stops are different. The 'R' model has beefier ones, meaning full lock comes a lot sooner. Even with that, I still get tire rub on the fender liners at full lock. My belief is that the main reason for the beefier stops is the wider wheels/tires that the 'R' receives. The T5 17" wheels are 7.5" wide and the 'R' 18"s were 8.0" wide. That little bit can make a big difference.

Just search "S60R turning radius" and you'll see keywords like "horrendous" and "laughable", or "might as well be driving a motor home".


----------



## coolsig (Jan 4, 2011)

I did check the fluid it had dropped below the min mark. Will need to top to the right level. As for the drop in rpm, it happens only when turning the wheel. 

Phew .... thats a sigh of relief. 

thanks everyone.


----------



## alex_at (Aug 13, 2011)

mine does it too. As far as I know it's normal. PowerDubs explained it right.

Rpm fluctuation also happens when I turn on the rear windshield defroster or try to close an already closed window with the button in the door. Should be normal.

The only thing, other than other cars, there's no rpm drop when I turn on the climate control.


----------



## IwasHuman (Jun 30, 2012)

alex_at said:


> mine does it too. As far as I know it's normal. PowerDubs explained it right.
> 
> Rpm fluctuation also happens when I turn on the rear windshield defroster or try to close an already closed window with the button in the door. Should be normal.
> 
> The only thing, other than other cars, there's no rpm drop when I turn on the climate control.


I think that's because the car knows to bump up the rpms a bit to counter that oncoming load. It has a second or two to get ready to adjust before it ACTUALLY kicks on the compressor. With the power windows, it's instantaneous power draw as soon as you hit the button, so it doesn't have that advanced warning. That being said, I've never really noticed it in mine. I'll have to test that out.


----------

