About 3 months ago, the clock started to spin wildly but it reset after a week. Now, three months later, I have the key in ignition but motor is off. Then it would not start. I called the tow and AAA said battery is ok. After an hour, the car started. I used it again and the next day in afternoon it would not start. I let it sit and the next morning it started and i drove it to the mercedes service shop. The technician said the battery (AAA 1/2021) was throwing voltages and not a mercedes battery. So, he replaced the AAA battery with two years of life with a new 1/2024 mercedes battery ($260 battery plus 2 hours labor). The same problem occurred after the battery was replaced. Then service technician checked the fuel pump, the starter, and key fob - all are working. Then he found the throttle body plate had a lot of carbon buildup. He cleaned the throttle plate ($900) and said if the problem continues he will have to replace the throttle plate ($1800). The same technician performed the B-service on the car and transmission service. When i got the car back, it was ok but i felt it didn't have a strong acceleration. In any event within 2 days, the same problem occurred. Car wont start at end of day. Is it a parasitic draw on the battery? or is it really the throttle plate? or something else. Yesterday, i drove 7 miles to work. then i drove 1 mile to pet store and then a short distance to another store. Afterwards it did not turn on. After sitting over night, this morning it turned on again. Any ideas on what is causing this intermittent start problem?

I have gone online and discovered that this is a known problem. Its basically engine cranks but does not start when it heats up. It starts fine in the morning. This morning I took it for a spin without any problem. Then it sat in the sun and again i turned it on for its second trip of the day and 7 miles later suddenly in the middle of intersection, it started to lose power and then it died. I had it towed to a mechanic shop. Waiting to hear back. Possible issues - fuel pump filter is dirty, spark plugs worn out, fuel pump relay is over heating (pins not aligning as it heats up)... any other ideas?

 

You 2008 could generate fault codes that can be checked. You did not say you checked those or had the mechanic check to see if there is any.

Now those codes don't pinpoint exactly but generally narrow down the area to look into.