Sounds like something is wrong here -- mixture is OK until you hit operating temp.

Check the resistance of the engine controls coolant sensor (don't remember which one it is, will have to look it up). If that is flaky, you will get a goofy mixture correction or ECU error due to impossible temp. Obviously, this one fails the ECU to max rich.

Make sure the air inlet temp sensor is connected, too -- this often gets pulled loose when the air filter housing is removed and someone yanks on the hose to the grille vent -- the temp sensor is in that area.

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!