My 2007 Mercedes S550 with 70,000 Miles has very erratic acceleration and shifting. Sometimes accelerates like a rocket, but often ceases that acceleration and barely accelerates at all for 10 or 20 seconds. Started about 3 months ago and is getting progressively worse. Now does it nearly every time I accelerate. I am working in the UAE. Local shop checked it with the computer several times and found no error codes. I replaced the Massive Air Flow Sensor with no improvement.

    Speed limit on the main highway here is 160 kilometers per hour or 99 miles per hour, if I press the gas pedal to the floor, it will very quickly accelerate to about 110 kilometers per hour and then the acceleration will drop off and barely increase at all. Letting off the gas pedal and pressing again will have little effect, when setting it on cruise control, it will have great difficulty. It will slow down about 4 mph and then kick in and speed up about 8 mph, passing the cruise setting by about 4 mph. Now it also acts up at most speeds. RPMs seem funny also. As though awkward gear shift signals are being given. Sometimes RPMs will be as high as 5,500. Other times as low as 2,500.

  Tried Octane booster and use the highest octane gas. No change.

 No warning lights or errors are on.

   I have ordered my own diagnostic tester, but it will take two weeks to get here.

  Could it be the wire to the Massive Air flow sensor?

  Could it be the accelerator pedal position indicator sending bad signals?

 Or could it be the turbo charger?

 Might drive to Abu Dhabi and have the Mercedes Dealer test it if my tester does not show an error code.


Ed Shorter


My guess is that you have a bad acceleration pedal. What you need to do a full system scan with star diagnostics scanner. 

Let us know what codes come up..

Thanks so much for your opinion. I was really close to ordering a new accelerator pedal until I noticed how irregular the rpm and gear shifting was. Research indicates the acceleration pedal or the automatic transmission Conductor Plate control module. I expect my analyzer to be here in the UAE in about 10 days. Hard to buy parts over here and a very high mark up on them. Just paid $4,000 for four shocks. Shops are a little hard headed and have trouble doing what you ask. Often they want to keep replacing parts till they replace the correct one. Thanks again!! Ed Shorter

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