My 2002 E430 seems to have an occasional miss at idle - for example, while stopped at a stop light the engine will stumble/miss maybe once or twice per minute.

There are no warning lights or malfunctions, but I took it to the dealership when it first started occurring (~3 months ago) and they of course couldn't reproduce it and said there were no malfunction codes in the computer.

The miss has gotten worse over the last month or so - any ideas on what it could be?

FWIW the car has 77k on it. Spark plugs were replaced at 60k.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE