vacuum pump (w123)
 

So I have an '82 240d with about 370k miles on the odometer. I've begun to notice that the engine doesn't quite shut off with the same authority. There's maybe a one second delay after switching off the ignition, then it will shut down with a quick shake. Should i be concerned that this is a warning sign of impending vacuum pump failure? Is it something that I need to address at this point or should i wait and see if it gets worse? Unfortunately my long time mechanic has retired and I'm hesitant to take it into a shop that I'm not familiar with (and that i can trust has the competence to work on these old diesels).

Are there some other, more benign issues that I should keep in mind for when i do eventually find a shop? From what I understand, there are no rebuild kits for the vacuum pumps. Any feedback is appreciated!

Before looking into the vacuum pump, I would double check the fidelity of the rest of the vacuum consumers. If it were my car, I would disable the central locks and see how the shutdown behaves, disable cruise control and see how shutdown goes, and then look into the vacuum shutdown actuator on the ignition assembly. Any reason to think the vacuum pump is bad aside from the delay in shutdown?

Edit: I didn't directly answer your question, but yes there are other issues you should look at (and can do yourself with a reasonable ease if you are level headed and willing). The vacuum pump supplies vacuum to several consumers. Any leak in those consumers (main line off the pump, brake booster, egr, climate control, central locks, ignition shut off, transmission modulator, few others I'm forgetting) would all have the ability to change how your shutdown occurs.

Normally a good vacuum pump will pull about 20” of vacuum. Temporarily insert a vacuum gauge into the vacuum line that goes to the power brake booster. Not to scare you, but vacuum pump failure can quite often do some severe engine damage. Also using a long wooden stick place one end of the stick on the vacuum pump and the other end of the stick near your ear with the engine running. Listen for unusual sounds coming from the vacuum pump. Be careful not to get tangled up in the drive belts. If you have a mechanic’s stethoscope that can also be used to hear unusual noises coming from the vacuum pump. ,

It sounds like a typical vacuum leak somewhere in the system. Do you have access to a mityvac vacuum pump tester?

Besides the mentioned vacuum leaks the vacuum diaphragm in the shutoff can become pores. If you remove the vacuum line of that and there is evidence of oil inside that is an indication of that.

There is also a vacuum switch on the steering Colum lock that also wears.

You have to begin by measuring the vacuum pump with all of the consumers out of the system. It's possible that a vacuum leak will result in low measured vacuum and an incorrect condemnation of the pump.

Not just those pesky vacuum consumers.
My 300cd had a crack in one of the (hard plastic) vac lines right at where they went through from the body to inside the pass door, right inside the rubber accordian.

Don't fault the pump until you test it alone with no vacuum consumers, say at the first main tube disconnected from the booster line. The trunk lock actuator is a common leak.

**update**

So after driving the other day with the a/c running, the engine would not shut off at all! Even after trying to use the STOP lever. Thankfully, it did shut down on its own when i got home. The vacuum lines for locks, trunk, fuel door were disconnected many years ago. The engine shut off vacuum unit was replaced in 2009. I'm really only beginning to learn about all these circuits and do not have the proper tools for testing vacuum. Hopefully i can get it into a shop soon for some diagnosis. I will ask to have the pump tested first, then go from there. The shifting is still pretty smooth, but brakes seem a tad harder.

Thanks all for suggestions and replies.

You can buy a hand held vacuum pump with a gauge for next to nothing. One hour at a shop is $100 and most techs working have no idea how to work on these cars.

Simply plug all of the small lines that come off the main line using a plastic golf tee. Connect your vacuum gauge to one of the smaller branches. Disconnect the end of the big line at the firewall and plug it with something. Your thumb will work.

Start the car and note measured vacuum. It should be ~15 inches or more. If less, make sure you don't have a vacuum leak in the line that is still connected.

Some hand held vacuum pumps come with rubber connectors suitable for connecting directly to the car vacuum pump where the metal line disconnects.

You either have a vacuum leak, bad vacuum pump or bad vacuum cut off. It is a simple system with well documented test procedures. Perhaps go to school - youtube university is one place that may be helpful.

Vacuum pumps were upwards of $300, becoming scarce even new without repair parts available the last time I checked a couple of years ago. You don't won't like paying an uneducated tech to buy, upcharge and install a pump at those prices - say $600 or $700.

These cars are old and thus very expensive for those who can't wrench.

I've had 2 slow to shutdown or no shutdown at all issues recently.
One was a torn 4 way X shaped rubber vacuum connector near the oil filter housing that has Brown, A bright yellow one way valve canister thing (Yellow goes to drivers door, Yellow with grey stripe goes to vacuum reservoir), and green with a yellow stripe coming out of it, and a grey hose feeding into it.

Brown on that connector is your shutdown "circuit", The yellow one way valve thing is central locking, green with yellow stripe is HVAC controls.

The 2nd slow shutdown I had was the floor vent pod, which is fed off that same 4 way X via the green and yellow hose that controls HVAC (goes through the HVAC valves and comes out as red with yellow stripe, should be the valve 2nd from left behind the hvac buttons).

The simple test is cap off those 2 "circuits", use a golf tee or such in the 4 way connector to leave just the brown connected, or use a mityvac on the brown hose to see if the shutdown circuit holds vacuum.