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

Most likely problem exists in the wires but finding the culprit will take a little time with a ohmmeter 2.2Kohms per wire only allowed a 10% deviation

Where would I connect the ohm meter to measure that resistance?

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

You would be removing the plug wires and measuring them end-to-end.

Your car is at just the right age & miles for the plug wires to be getting a touch flaky. About 7 years is how long the M112/M113 wires seem to last. Idle quality degrades first, though it takes a while to throw a code.

I had the same symptoms on my 2001 E320 - an occasional, single stumble at idle. The problem was somewhat correlated with wet/humid conditions.

Replacing the plug wires eliminated the occasional stumble.

- JimY

I have a stumble under load that one mechanic said is plug wires and another said is fuel injectors . How do I differentiate between the two?
Car is a 93 400 SEL