PeachParts Mercedes-Benz Forum - View Single Post - My diesel is dieseling (doesn't shut off promptly)

ljsense · #6 11-20-2007, 10:57 AM

I just went through this. You'll probably find better instructions if you search the forum, but here's my take.

1. Ask yourself if the problem started after an oil change or some other work under the hood. If so, you probably just have a disconnected vacuum line. look for a plastic line that is not connected to a rubber tube or fitting. Quick, easy fix.

2. If that's not the case, pull the plastic line off your vacuum shutoff valve. (As another said, it's brown and goes from the firewall down behind the injection pump to a little brass colored can.) If there's black oil in there, it's pretty likely your shutoff valve has failed. The part is around $50, and pretty easy replacement on a non-turbo. Order it and two paper gaskets.

3. If you've got oil in the line, it might be causing problems elsewhere. So you might wind up having to replace the ignition vacuum switch. That's kind of a chore, but doable. (I posted instructions about a week ago.)

4. You might just have a vacuum leak somewhere else. Get both a vacuum pump and a vacuum gauge and get into an analytic, detective sort of mood.

Overall, your vacuum pump generates vacuum. It goes first to the brake booster line, that thick black tube that runs from up front near the radiator to the drum shaped thing near the firewall. You can test any fitting directly off it to see if it's pulling vacuum -- should register 20-some inches. Then test various points on the shut-off circuit. See what's happening. Maybe your door lock system is leaking.