On a K-Jet system this behavior is usually a vacuum leak, typically a hardened or split idle control valve hose or a petrified air meter horn the throttle body boot.

All those parts must be flexible, if they are hardened you should replace them.

I fought this battle with the TE, and finally even ended up replacing the o-rings on the fuel injector holders that no one knows exist.

Also check for the condition of the ignition wires and spark plugs, as bad ignition will result in improper fuel mixture, at least when warm.

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!