Try tapping on the OVP relay (behind cover behind battery, red fuse on top) when it's idling too high. If the idle returns to normal, replace the OVP relay, its' bad.

However, it's more likely the idle control valve is bad. Clean before replacing -- remove valve from car, fill with carb cleaner and cover the two holes, shake a bit, dump, and refill until the stuff comes out clean and re-install.

Otherwise, you have a computer problem that will have to be proberly diagnosed. You will need to check the EHA current and the duty cycle, verify that the O2 sensor is working problery, and that the mixture is correct. See the DIY article in the DIY forum, it helps.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!