Originally Posted by jaoneill

this makes no sense. I had some shutdown problems with the 300sd a month or so ago, vacuum output was marginal, so I installed a new vac pump. This appeared to solve the shutdown problem; until now. Problem cropped up again the other day - turn the key off and the engine keeps running.

Got out the trusty mity-vac this afternoon and things got interesting. I disconnected the vac line at the shutoff valve. When the mity-vac is connected directly to the shutoff valve the engine shuts down at about 12 in.Hg; this tells me that the shutoff valve is ok. Next I connected to the vac line - turn off the key and the gauge jumps to 23 in.Hg; this indicates what should be more than adequate vacuum to operate the valve. Installed a new connector, line to valve, started the beast, turned the key off and the bloody thing didn't shut down.

I repeated the test procedure three more times with the same results - any ideas would be most appreciated.

Thanks, Jim