My car had a problem like that when the O2 sensor connector was seeping voltage to the heater connections. Don't ask me how this happened, but I fixed it up and the problem has yet to come back. It happened once the car was all warmed up since that's when the O2 kicks in.

Also check the fuel pump, is it buzzing really loud? Does your car give codes? Try monitoring the EHA current to see what it does when the problem occurs.

xp

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1985 190E 2.3L - a constant project.