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Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 54827
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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Hi - I have a Merc W220 S500 auto 53 reg. I have had trouble

Customer Question

Hi - I have a Merc W220 S500 auto 53 reg. I have had trouble with an apparent stalling when at say 5mph or when starting from a traffic queue. The 'misfire' is not always constant - day to day and then when it continues there is a problem in changing gear from 2nd upwards - requiring 3000rpm before a change. Then after a while the engine problem lights up on the dashboard and I have of course taken it to my Merc man (properly trained and with the correct computer solving equipt) He thought after the initial check is was an air mass filter which was replaced (twice) but to no effect. Another trip to him and checks done again with no apparent problem - it did not go away. He has sent the computer control unit to a specialist and there appears to nothing wrong with it. In the event it may mean I have to pay £1,000 for a new one - have you any thoughts about another possible cause? Thanks - Ian
Submitted: 4 years ago.
Category: Mercedes
Expert:  Marty replied 4 years ago.
Hi Ian, my name is Marty. For an intermittent problem like this I would check for a possible fuel pump problem. It sounds like you may be losing fuel pressure intermittently. The mechanic should also check for a poor connection to the mass air flow sensor. If he had fault codes pertaining to a faulty mass air flow sensor it's possible that the connection is faulty and not the sensor. I've received my share of bad air flow sensors in the past as well. If he is not using original Mercedes mass air flow sensors he may want to try that. He should also check for intake manifold leakage by smoke testing the intake system. I'm assuming that the overall tuning has been checked already. If you are getting occasional misfire codes he should also check for a plugged catalytic converter, especially if the misfire codes are all on one side of the motor. A fuel sample should also be performed to check for contaminated fuel.

Please let me know if you have any questions.