The problem I am having is an intermittent one, making troubleshooting particularly vexing.

The engine is an '85 617.952 with the EGR and ARV disabled. The chassis is an '85 107.

The symptoms are

1 Difficulty with shutdown - Occasionally the car is difficult to shutdown, either doing so slowly or a couple times, not at all (used the manual shutoff). Sometimes revving the engine a bit helps, other times not. The shutdown is a manual setup with a vacuum solenoid allowing vacuum to the shutoff valve when a switch on the dash is pushed.

2 Clunking into 1st gear when slowing down to a stop

3 Hard 2-3 shift on acceleration

These symptoms work in tandem. If I'm slowing down with the intent of shutting the car down, if it clunks, it's going to be difficult to shutdown. If there is no clunk, it shuts down normally (or close to)

Just got back from a 5800 mile road trip where things worked properly 90 plus percent of the time. Then on the very last leg it refused to shutdown completely. The symptoms would randomly appear and disappear seemingly at will.

I've checked all the rubber hose connectors for any obvious leaks and they appear to be fine. Brake pedal is always normal; no hard pedal. Door locks always work properly and the reservoir holds for 5 or so cycles as it should. Trunk and fuel locks all work.

I used a mechanics stethoscope on the vacuum pump and there are no unusual sounds.

I've checked the routing against the vacuum line diagram and all the orifices and dampers appear to be in their proper place and the lines connected as they should.

I haven't checked recently, but last time I did, the transmission vacuum control valve functioned properly.

I've tested vacuum at the following points with the readings shown. The 12 inches is steady state and it drops to 10 upon acceleration - presumably due to the transmission VCV doing its job.



And things can be extremely random. For example, we stopped for dinner last night and the car wouldn't shut off. Used the manual shutoff on the engine. Then after dinner, started the car and, as a test, immediately hit the shutdown switch and it shut down completely normally.

It seems like I've checked everything. I have a spare vacuum pump I'm planning to rebuild as soon as I can source the proper bearings, though that doesn't seem to be the problem.

I'm out of options and open to suggestions and ideas.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica