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Discussion Starter · #1 · (Edited)
Waveform-like surging under acceleration at any speed - SOLVED

Hey folks!

Well, it's day 2 of ownership and she's acting up. :frown:

As the subject described, under any level of acceleration the engine surges up and then returns to normal, then up, and returns to normal (the duration is 1-1.5 seconds). In other words, it's as if I'm playing with the throttle by lightly gunning it to the beat of music - this is why I used waveform-like as the description. I don't detect the supercharger clutch engaging/disengaging as the feeling of torque is always present, if that makes communicates.

Now, she idles smoothly and there are no sputters or surges once I enable cruise control (maintaining set speed). If I use cruise control to accelerate, there doesn't appear to be any surging at all. And, no warning indicators are present on the instrument cluster.

In bullet points:


  • Silky smooth idle
  • Surges up and down under any level of acceleration
  • Can accelerate with cruise control with no surging
  • No warning lights are present - waiting for OBDII sensor (arriving this weekend) for possible codes
  • Car failed emissions test... apparently.

Does this point to a faulty accelerator pedal assembly (drive-by-wire)?
 

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Discussion Starter · #4 ·
Any ideas? I realize not everyone will receive a reply to their posts, I'm just looking for tips and initial direction.

Many thanks!

P.S. I should have my code scanner by this weekend; I will update the post with codes at that time.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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What scanner did you order? Do you have a CEL on?

Interesting symptoms, especially the "cruise works, pedal doesn't".
 

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Premium Member 2012 SLK350
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Does this car have a pedal position sensor or is it a cable linkage?
 

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Discussion Starter · #7 ·
Thanks, guys.

I don't have any CELs present, and I do have the position sensor-based accelerator pedal. Part# 1703000104 (here's a link for reference)

Regarding the scanner, I ordered 2 bluetooth OBDII dongles (both were recommended units with the Torque Pro android app).

A neighbor thinks it's the sensor, and I would agree, it's just interesting that there's no CEL or other indication.

Is it safe to assume that this would jack with air/fuel ratios as well given that the ECU doesn't know what's going on? Mileage seems to be on the low end of efficiency.
 

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Premium Member 2005 SLK55 AMG; 2005 SLK350
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You really need an advanced scanner to test the accelerator pedal -- the OBDII is just too basic for the task since it only covers emissions and not internal logic.

Why did it fail emissions?
 

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Discussion Starter · #9 · (Edited)
Thus far, everything I've seen that's reasonably priced is OBD2 based and only the software differs. Which scanner do you recommend for pulling codes? I hope you're not going to say Star. :)

Emissions showed rich mixture, unless the seller falsified the results of the test.
 

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I would start by cleaning the MAF sensor. Just get a tin of MAF cleaning spray and follow the directions on the tin. Simples! Worth doing even if it doesn't cure the fault.
 

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Discussion Starter · #12 ·
My vehicle doesn't have a MAF (it utilizes a MAP sensor), otherwise I agree that cleaning the MAF certainly would have been the place to start.

I'll update this thread with codes this evening, assuming the dongle(s) work and the software can actually retrieve all of the information.

Thanks again,
-M
 

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Discussion Starter · #13 ·
The Bluetooth dongle was just south of complete garbage and works intermittently at best. The Torque Pro application is awesome, however...

I have an iCarSoft i980 en route (used - heck of a deal) to me and will, again, update this thread with information.
 
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