Got myself a runaway diesel. The symptom/findings are:

• Vacuum pump tests OK (>20 in at power break booster)
• Stop lever on IP stays in up position (car off or on). Pulling vacuum on the stop lever makes it go down. Pushing the stop lever down will shut off the engine off. Obviously, the stop unit is working fine, just not getting any vacuum.
• There is good vacuum at the inlet to the brown vacuum line that runs from a T-connection off the brake booster main line to/through the firewall. This brown line has no connections before it goes through the firewall.
• There is no vacuum in the brown striped line that connections to the stop unit on top of the IP. There are several rubber connections in this line after it comes out from the firewall, with no vacuum on this line tested at each rubber connection
• I plugged the yellow and green vacuum lines (power window, climate control), with no change in the stop unit vacuum.
• It appears there is a vacuum leak somewhere in the car interior (inside firewall). Where to go? Where to start?

are you running an aftermarket with a possibly aftermarket/modified unit?

Pull the gauge cluster and check the connections at the key switch. Check that the key switch is closed with the key in the run/2 position and open in the off/0 position.

Not sure what you mean that the stiped brown line has attachments. Are there splitters or did someone splice the line with rubber hose. IIRC it shoud run uninterrupted from the key switch to the shut-off actuator.

Sixto
87 300D

Pull the gauge cluster and check the connections at the key switch. Check that the key switch is closed with the key in the run/2 position and open in the off/0 position.

Thanks. How do you remove the gauge cluster?

Not sure what you mean that the stiped brown line has attachments. Are there splitters or did someone splice the line with rubber hose. IIRC it shoud run uninterrupted from the key switch to the shut-off actuator.

The striped brown line has no interruptions ( no tees or splitters) between the firewall and the shut-off actuator. It does have a 2-3 inch section of black rubber hose between the firewall and actuator, but that hose just connects two section of brown line.

Search and ye shall find

http://www.peachparts.com/Wikka/W124InstCluster

Sixto
87 300D

sixto - you are the man, thanks.

so the cut-off vacuum tube should be visible and accessible with the dash cluster removed?

To me there is better access through the gauge cluster cavity. Some might prefer access from below. Since pulling the cluster takes but a couple of minutes, I'd start with that.

Vacuum line is just vacuum line. The key, I think, is to test the key switch itself.

Sixto
87 300D