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Our ’02 ML 500 with 115K miles, intermittently hesitates for a second or two when the accelerator is pushed. It is like there is a delay between when the accelerator is pushed and when the throttle is opened. Pushing the accelerator further does not seem to make the engine respond any quicker. There are no lights and no engine codes. The first time this occurred, the service folks replaced the Accelerator Pedal Sensor (Accelerator Potentiometer) and serviced the transmission. The truck ran well for 1,500 miles, and then developed the same symptoms. The second time, again with no lights or codes, the wizards again replaced the Accelerator Potentiometer – they claimed the first one suffered infant failure. Now we have approximately 600 miles since the second potentiometer was installed and the symptoms have returned. The professionals do not seem to be able to isolate this problem. The fuel pump was replaced 11 months ago. Any observations will be sincerely appreciated.
 

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Just curious what work (ncluding maintenance, service and repair) was done in the 90 days preceding the first onset of this symptom? May be irrelevant, may be important.
 

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Just curious what work (ncluding maintenance, service and repair) was done in the 90 days preceding the first onset of this symptom? May be irrelevant, may be important.
The front breaks were replaced 35 days before the first occurrence. The second prior service was fuel pump replacement 180 days before. The truck was not driven much this year, my wife visited family while I was in Afghanistan.
 

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You may want to use an OBDII scanner to see if there are any pending codes (which will not light a dashboard problem light unless it repeats itself certain number of times).

If you have a decent OBDII scanner, you can monitor live the engine parameters and see if there are any anomalies in the list or behavior of the engine throttle/MAF/etc parameters.

In the earlier ML's sometimes the fuel pump could not deliver gas fast enough and it caused hesitation without an engine light..

AC
 

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Research the archives on the throttle position sensor. Several months back someone had a problem starting the vehicle and the instructions for calibrating the sensor were posted. The thread started out with something like the vehicle was left at a stadium and the poster kept trying different suggestions to get it working. The vehicle would start but then either die or would only creep along (I don't remember which). This should give you enough information to find the thread.

Good luck!
 
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