'02 ML 320 - Engine Hestitates on Acceleration
 

'02 ML320 (163.154), 65K miles... has had a recurring fault where the engine seems to hestitate on acceleration. The vehicle has been seen by the local dealer on 3 separate occasions for this complaint, yet the fault persists.

On the last two visits the dealer flashed the engine control module, performing "31WLT40" and "275WLT40".

Any idea as to what these numbers refer to?

Thanks.

Has the car been serviced? Spark plugs at 5 years?
Fuel filter?

Has the dealer ever replaced the air mass sensor?

Vehicle has been well maintained - fuel filter at 60K miles, spark plugs (003 159 94 03) at 5 years (52k miles), air filter at 30K and 60K miles, engine lubrication every 7.5 K miles, with synthetic oil and fleece oil filter.

Air mass sensor has not been replaced... dealer has repeatedly stated that it is not faulty. No fault codes have ever been present; have no idea what the real time data shows.

Since 2006, has a newer software version been issued?

The vehicle has had this intermittent problem since new, which persists despite the two software updates.

With the high % of air mass sensor problems & replacements required, I would start with a new one.

ML320 Hesitant
 

My 2000 ML320 had same problem, and it turned out that there was not a problem with the engine. My A/T transmission fluid level was too low! Make sure your fluid level is at "HOT" all the time! Buy a dip stick and check fluid level yourself.