check these items

do a fuel pressure test, check for internal and external leaks, air flow sensor plate and the coolant temperature sensor.

I fixed a stalling when warm problem with a new coolant temp sensor and fixed some leaks at the fuel pump assembly hoses. The resistantance is measured diagnolly( if you have a 4 pin coolant temp sensor) and the resistance MUST be the same or its junk.

Are you plugs black?

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)