1985 500sel diagnostics
 

It's been ages since I owned a CIS car and I need to remember a few things.
This is a 500sel that cruses on the highway very well, but when she's warm, idle stumbles a bit and can stall when I try and pull away at a traffic light.

There's got to be an old thread or two here that would help me in diagnosis, but with lots 90's 500sel threads in the way, I didn't find them.

With warm regards,
-CTH

I would start with cleaning the cap, doing a smoke test, checking ignition wires, plugs etc...

If you're looking for other threads then the system you have in your 85 is similar to 81-85 380 SL or SE or SEL or 380/500 SEC

to diagnose it, you need the right pressure test kit. then you can see what's going on.

that I have, but I've not dusted it off yet. I was hoping somebody had a procedure to use it with tucked away in a thread here. -CTH

It's a good call to check the pressures.

Your best bet is to get a factory service manual because it will have all the values and you will have to check a number of readings:

System pressure (Pressure regulator is built into the distributor on your car I think)

Control pressure (WUR off, WUR on, Disconnect and Connect Vacuum to WUR)

Pressure leakdown.

You also have a Frequency Valve which works in conjunction with the o2 sensor and the ECU to bleed down the control pressure. It's basically a "fuel injector" with Control pressure at the inlet and a fuel tank return on the "injecting side".

But as I've mentioned in post #2 check the simple stuff first