Diesel engine "run-on"
 

I have a 85 Mercedes 300SD engine #617.951, and about a week or so, the only way that I could stop the engine from running, was to pull the hood open and hit the stop switch, even though I had already turned the key off and gotten out of the vehicle.
Is this an old "shady-tree" mechanic can fix or do I have to do the "two step" to the dealer????
I can be reached at playergb@yahoo.com or freight786liner@aol.com.
Would like to fix ASAP 'cause it is getting tiresome putting my arm in the engine compartment after pulling up the hood.

Can someone help me?????

You probably have a vacuum leak. It should be a diyer type of repair - the hardest part is finding the leak. I would suggest purchasing a vacuum pump kit - the "MightyMite" which is available about anywhere is a good one. Also, look around REAL good under the hood in the vicinity of the brake master cylinder and you may even be able to find disconnected vacuum lines or broken rubber vacuum line connectors. It would help too to have a manual showing all the vacuum lines and their colors. If it is not a vacuum leak then it is the shut off mechanism in the fuel injector that is controlled by vacuum. Also, do a search on here on vacuum leaks.

On my 83 300SD the shut off valve vacuum line is brown in color. Here is an easy way to determine if that is the problem of "shut off mechanism". I don't think 85 vacuum digram has that much difference.

if you don't have a vac gauge...

Locate the main vacuum line connected to the brake booster, you should see two vacuum lines(one is brown and the other one is white) connected to a Y connector which attached to the T connector of the main vacuum line. with the engine running turn the key to "off" posistion(or remove the key from IGN) to shut it down. Now, go out there and disconnect the "White" vacuum line and use your finger to plug that open Y end. if the engine shut off then there is a leak somewhere else that the white vac line goes... If the engine doesn't shut off, disconnect the brown one too and put another finger on top of that open end to see if there is any suction...if not then the T connector is clogged.(assume the pump is working since you didn't mention brake is hard). If you feel the suction then locate the other brown vac line on the wall next to the brake booster mounting surface and trace it down...it should be connected to the"shut off mechanism" on the back of the IP. disconnect it from there and connect a spare vacuum line directly to the Y open end, close the end with your finger. it the engine turn off then there is a leak where it connect to the IGN switch. otherwise it's the"shut off mechanism"

Sometimes you can find diagrams in some to parts catalogues.

The easiest fix is finding something recently disconnected under the hood (this is likely if it happend all of a sudden rather than gradully getting worse and worse). The next place is to pull up the floor mats for the driver and begin testing lines with the vacuum pump.

If you don't find anything, pull up the floor mats on the front passenger side.

There are two vacuum tubes for each valve... one to open and one to close. The lines are color coded for the open/close

It is not hard, just a real pain trying to track it down. Then usually taking off the door panel to access the affected valve. Definately a DIY. Just be patient.