91 500sl. Starts and runs fine for a few miles then starts sputtering and usually dies. Most times will start right up again...
I have same model /year, but need more info.
Any fault codes? Keep ignition on after engine dies and check codes. (They reset when you turn ign off).
Does it die just at idle, or on throttle, or both? (Can you keep it running with the throttle?)
Has it stood (dormant) for several months prior to this problem?
Yours is the KAT version?
Do revs rise at idle to 900/1000rpm before engine dies?
Can you smell gas fuel just before it dies?
Do you hear a click from engine compartment when you turn off and reset the ignition after it has died?
Reason of further questions:-
Clicking noise can indicate faulty fuel pump relay, and because this is incorporated in the MAS module as Albert said, possible faulty MAS controller. You can read codes from MAS. "Fuel pump relay (circuit 87) not functioning" indicates faulty MAS. When you reset the ignition, error clears, and you can hear a loud click from MAS unit when relay resets. This could be why you can restart right up again. You can remove MAS and clean terminals. Sometimes this works. I blanket soldered the PCB which seemed to fix mine. (I had fuel starvation at high revs - different to your problem).
Faulty FPR (fuel pressure regulator) doesn't maintain fuel pressure when ignition turned off, and also dumps unmetered fuel into inlet manifold. Symptoms are difficulty starting, particularly longer you leave (~24hrs), and lumpy idle on start up. Usually clears on throttle.
Because it starts right up again, probably not FPR or distributor caps, but worth checking and cleaning anyway. Known issues, but not aligned with your symptoms.
Revs rising would indicate air leak (if you have the KAT version).
As engine dies after warmed up, most likely heat related in electrical component, or maybe over fuelling due to loss of vacuum to switchover valve.
Possibly CPS (crankshaft position sensor) but usually not that critical on older CIS systems, I believe.
If you can keep it running on throttle, this would indicate fuel mixture issue. Maybe leaning out when hot, but probably not likely because it starts right up again.
I think this is error code territory.
Regards
Rob