If the car starts and runs for 10 minutes, and if it runs fine, like smooth and responds to gas pedal, and at idle if the rpm can be raised to 6000 or so without misfiring or hesitation or excessive white smoke at the exhaust, it cannot be the ECU. It is also not the OVP relay, the job of this relay is to cut off the electrical circuits in case of over voltage, which if the RPM are raised should occur at idle even in the first 10 minutes. If it does cut off on high RPMs at idle in the first 10 minutes, then the alternator is sending a high voltage, chenge the voltage regulator. It sound to me like there is a temperature related problem, either there is some non-metered air going into the ait intake or your idle valve is bad or you have a bad fuel injection temperature sensor, the temperature sensor was definitely a problem in my car (87 260E) at one point and gave the same symptoms.

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Saumil S. Patel