Hello To All,
I finally found my '89 Mercedes 300 Wagon, a car I have admired for several years. I have a problem though, and was thinking perhaps one of you might have an idea before I go head on with it. The car starts and runs well until the temp needle just begins to rise. Then, the car will stumble and eventually stall. Starting again is hard, but it will start with some coaxing. Anyone have a clue as to a sensor problem? Car has 250k well maintained miles.

Guessing this a gasser?

sounds like it could be once it hits closed-loop its having issues. Start with the basics if you have no history of the following -- Plugs/wires/rotor/cap/o2 sensor/idle air vacuum hoses.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

X2. With emphasis on the plugs, cap, rotor, wires.

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Eugene

10 E63 AMG
93 300te 4matic
07 BMW X3
14 Ford F-150 Fx2

Also check the air flow sensor potentiometer for dead spots. Mine was doing the same thing, however it would not stall.