Uh-oh. Key not working to turn car off
 

My car is an overachiever. It rebelled when I only drove it 1 mile today.

I turned the key off, and the car keeps running.

This is not a Shut Off Valve problem, though I did have to use that to shut the car off. This is a key problem. With the Shut Off Valve, the car would "sort of keep running", and I've already replaced that a few years ago. This is where I turn the key off, and the car continues to run perfectly.

Soooo, I'm guessing this is a key tumbler problem, and if so, what to do about it? My key comes out, and it stops in the normal position in the tumbler. The only other thing I can think of, is that in the proper "Off" position, the car is not getting the signal to knock it off!

1991 300d, 169k

It may not be the tumbler, It might be the tongue or tang that the timbler fits into. It could be worn to the point the tumbler doesnt activate it. just guessing.

I was looking at an old one I have with the tumbler out.
maybe remove the tumbler and see what it looks like down in the recess. try using a flat blade screwdriver to see if it will turn the engine off. should be able to start and stop the engine with the screwdriver.

Charlie

If the key is in the lock position (all the way counter-clockwise) and it keeps running, you have a vacuum problem, and NOT a key/tumbler/lock problem.

Did you replace the Shutoff Valve on the Fuel Injection Pump or the Shutoff Valve that is mounted on the Steering Colum lock?

As ROLLGUY said there is always a chance there is a vacuum leak somewhere. All of the Plastic Vacuum Tubings are connected with 25+ year old Rubber Hose.

When I did my first Oil Change I did not realize I leaned on the Main Vacuum Line and cracked off one of the Platic Nipples. My Engine also would not sutoff with the Key when that happen.

Troubleshoot the simple stuff first.

Vac problem??!
 

That might be it. I changed a fuel pre-filter the other day, and accidentally moved some of those wires that run in that general area. I'll take a look at those tomorrow.

He said it was not a shut off valve problem, and it was replaced a while back.
Also didn`t mention any other Vacuum related problems like door lock functions.

Vac could be applied to the shut off valve to see if it works, or suck on it.

There was a thread a month or so back where the was the problem I mentioned above.

Charlie

Door locks work
 

I checked the vac lines and they SEEM to be all plugged in, but it's hard to really find that out, since they're nearly unmovable, with the hard plastic casing, bundling maybe 5 of them together. Might have to take it to a shop.

Don't bother taking to any shop. Save yourself some money, and go buy a Mightyvac (or other brand vacuum tester). There are plenty of knowledgeable folks around here that can help you find the leak. Vac system problems are common with these cars, and are very easy to trace and fix with the help of a vacuum tester. No MB owner should be without a Mightyvac!

Vacuum for the door locks on your car is produced from a pump under the rear seat. It is not connected to the vacuum pump on the front of the motor.

I fixed the same problem! In my case it was the vacuum swwitch that attaches to key assembly. It was a pain to get that to where I could work on it. You should be able to verify this using the Might Vac. There is a brown vacuum tube going in and out of the firewall. The supply comes off the main supply to the brake booster right before it goes through the firewall. Don't try to remove the vacuum tube from the brake booster or you are going to have to replace the brake booster supply. The shut off vacuum gets its supply from the brake booster line. It is obvious where it branches off. Don't try to remove the tube!

Make sure the brown line is hooked to the shut off valve. If it's not hook it up. If it is, unhook it and replace it with a length of vacuum hose. Start the engine. Suck on the hose. If it shuts off with 3 or 4 strong sucks, the shut off valve is ok and there's a vacuum problem somewhere between the source and the shut off valve.

That is a very simple circuit though. The circuit is Brake booster, to vacuum switch in the ignition to shut off valve. No other elements are on this circuit.

Had same thing happen to my 86 300sdl this week when replacing a rubber 4 way connector i apparently leaned on the line running to ignition. Luckily found it within minutes but can imagine how frustrating it could have been. Id definitely say start with the vacuum lines as almost all mine snapped to the touch

Problem found
 

I had the Mity Vac, rented one actually, from Auto Zone.

The Shut Off Valve, I just replaced that 4 years ago, so that was fine. Checked all the vac lines, they were all in tight. Finally found the culprit. It was a hose on the driver's side, about 2 feet back from the front of the car, under some gizmo. The hose was dryrotted really bad. Replaced that plus a few others, and problem is solved.