W126

My 1984 300sd will keep running after the key is out of the ignition. I do have a new shutoff valve to replace, but have not gotten to it.

Well, I figured out why the engine cuts off some times before I get the hood up. When I'm getting out of the vehicle I tapped the brake and it killed the engine. I do this with regularity now. Has anybody heard of this? And if so, is it still my "shutoff valve" or a vacuuum booster to the brakes?

Idle problem getting much worse.
Help if you can. My '87 6cylinder SDL is a little different than older models. However, my idle is driving me nuts. The car has been running great for years. Last month every once in a while when Hot the engine would Rock/Roll at idle. That idle problem got worse and worse. It is intermitent & used to only happen after the engine got to hot operating temp. Now it happens at all temps and is still intermittant. Sometimes it idles just beautifully. I've inspected the entire fuel system, replaced most of the hoses and clamps, replaced the fuel Pump. My IP is a little different than pre '87 Mercedes, so I don't have a dampner bolt and my ALDA looks different than older models.
Any suggestions on what to try and adjust?

Hey guys and gals.

1984 300SD
142k miles
I have had it about 8 months
I have changed both fuel filters and purged about 5 months ago.
It has a fairly fresh oil change and filter about 3 months and 3500 miles ago.

It starts and runs very easily and well.
It kicks down and shift correctly (sometimes a little jerk on upshirt but really minor)
All my vacuum stuff works

When I drive the car it start and warms up to 1/4 the way above 80deg on the temp gauge and stays there if it matters.