I am having a hard time locking my 91 300TE. I use my key to lock the car and the after the driver's side button goes down it comes right back up. The other doors (passanger, rear, hatch and gas filler door) all would not lock. I sometimes have to walk over to lock the car on the passanger side and than all the doors would lock. I also tried to reach over from the passanger side to manually lock the driver's door but the button would pop back up again after a second! I can hear the vaccum pump running when all the doors would lock from the passanger side.

it may just be a vacuum line, cracked or damged.

it could also be an actuator.

when mine went it was a vacuum line problem. i had already bought the actuator.

you may be able to find more info on a 'search'

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*92 400e 124.034, SOLD

*92 300e 124.030, SOLD

I'm not sure if this is common but I've seen that happen on most of the older models. This does point to faulty actuator or vacuum situation on the driver's side door. However, if you started to trouble shoot that you're bound to end up with more than $100 to $200 worth in labor and parts. easiest thing to do is either to use the trunk or the pass side to lock, or you can invest in a remote lock/unlock module for around $100 and make life easy for yourself. this way you won't have to bother using the key at all. just a suggestion. atleast that's the route I took.

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