Car: 1986 300E

Day 1 - Driving down the highway at 60-70 mph, engine suddenly cuts out. I pull over to the side and start the car. Car starts and all is fine.

Day 2 - Same thing, drving on hwy at 60-70 mph. Engine cuts out. The engine is being driven by the transmission now - I didn't switch the trans to neutral. Without thinking, all I do is turn the ignition off and turn it back on (did not crank the starter) and the engine fires right up and no problems.

Day 3 - Same thing. But this time, I pulled over again and tried to start the car. After about four of five tries, the engine came to life and it ran like a champ.

Temperature on all three days was about 50 degrees. The stalling happened after drving about 12 miles from work out of which 7 are on the highway usually driving close to 68mph

What could be the problem? Is is fuel delivery related - vapor lock, or clogged fuel filter, or bad fuel pump/fuel pump relay.

Thanks

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold