New to this forum. I have a 2005 S Type that I recently purchased. Sounds like running over a rumble strip and feels like a misfire although I think it is related to transmission. Can anyone help me? No codes. Have had several shops look at it with no answer. A Mercedes shop told me it is a bad torque converter.

 

A bad TQ will set a code.
Rumbles point to wheel bearings and tires.
Have you changed tires?
Have you rotated tires?
Is the noise from the from the front or the rear of the car?
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That sounds like cattle gridding, the sensation of travelling over a cattle grid or rumble strip. It's caused by a bad TC I'm told.

 

On the S Type the bad TQ will lock and unlock rapidly giving you a surging feeling in the car.

Best way to check is with a cold engine set the cruise about 45 mph. Then watch the tach to see if it wavers up and down about 50-150 rpm. It should set a code?
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Mine wavers up and down 150rpm on downhill runs and is most noticeable when engine is at temp. No codes show.
I was told the TC could be on the way out, so just waiting for it to get bad enough to be diagnosed properly.

Yours could be going the same way.

 

Thanks to Mannycars and Tbird. Rumble strip sound and surging occur at different times. Both go away with slight acceleration or letting off of the gas pedal.

 

If it's the torque converter, is there a way to disable the lockup feature for troubleshooting? Perhaps the fault is just below the threshold that sets the code.

On my '02, I was under the impression downshifting from D to 4 (across the bottom of the J gate) doesn't actually change gears, but simply turns off the power to the clutch in the torque converter. I know the shift cable doesn't move when shifting between D and 4, but there is a microswitch in there that clicks. Not sure if I'm even close with this idea, or if it's even the same on your '05, but hopefully somebody else could weigh in.

 

Is it possible they could be 2 or more different issues?

I'm thinking as per Tbird6 that the rumble may be either wheel bearings / tyres.

The surging that disappears when either accelerating or easing off the gas....perhaps 02 sensors ( depending on age / mielage of course )

 

If you run in "4" and it goes away ... torque converter.

On the Merc transmission, the "4" position inhibits torque converter lockup and inhibits shifting to 5th.

 

Snag is... S-Types don't use the Merc trans.

The PCM largely determines which gear the trans (ZF 6HP26) is in, together with the TCM (in the trans).

Worth doing things (like rotating tyres front/rear) to rule out cheaper and easier to fix possible causes. So far it does sound like the TC.

 

What speed?
What gear?
Turning/going straight?
Hot engine?

 

Around 50 mph slight load on engine. Engine not running hot.
I tend to believe it is the torque converter, although the noise and surge occur at different times they both go away when you accelerate or let off of the gas.

 

Is there any movement in the tachometer reading, or is the cycle too short to register?

 

Next time I drive the car I will have to pay attention to the tach. I just purchased the car recently and it has been in the shop more than in my garage.

 

Just got a call from an independent shop, he ran diagnostics on engine and transmission.
Says the MAF needs cleaning and no codes on transmission. He said the bushing in the lower rear control arm is worn and thinks that is what is making the rumble strip sound.
Does that make sense to anyone?

 

He wants over $900 to clean MAF and replace lower control arm. I don't know if I want to spend that kind of money and maybe not fix the problem.

 

Doesn't sound like a suspension issue going by your description and that's a lot of money he wants to do those jobs, even they need doing.

 

From what I gather both the rumble strip sound and the surging issue point to TC issue.

 

'fraid so. I'm in the same boat, with two automatic 'specialists' not seeing any issue and one saying it's 'possibly' the TC. Not really the sort of item you want to change on a whim, so I was simply advised to monitor it.

 

How comfortable are you with this shop? More importantly, what is their "return" policy? If you're hiring them to diagnose and correct a noise, what will they do if their diagnosis is incorrect? Some (but not many) shops would credit that repair towards whatever the final fix may be, be it the torque converter or the decomflagulator bypass modulator valve.

No idea if the MAF sensor could be part of the equation, but I doubt the suspension fault would make the noise you've described. From my experience, worn suspension parts cause clunking, especially at lower speeds, and sloppy handling. I've never had one make a buzzing sensation, not that it's impossible.

Did you ever get a chance to drive around with the transmission downshifted one notch from D? Even if the TC control logic is different compared to my '02, the results may still provide a big clue.