My aunt has a '99 E430. If you recline the passenger seat forward, it takes off and keeps going forward as until it's up all the way. What could this be?

I appreciate any help on this matter since it's obviously a great inconvenience. I've never worked on a w210 before.

Best Regards,

David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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The motor is wearing out or the plastic gear(s) is broken. Experience has taught me...it's usually the plastic tooth gear....it could be the actual motor or the rail/track gear.
Another possibility...the switch is stuck....I use air and blow out the crevices in the switch...the "can air" used to clean out computer keyboards...if I use the shop air...I make sure I am at least a foot or so away...too high pressure....you'll blow or break the switch apart.

I would start by removing and taking apart the switch on that side. I believe a search will reveal a DIY article on how to take apart the switch and clean it.

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1989 300CE