CLean the throttle body. The gasket for this is $1. A couple cans of carburetor cleaner is another $5. Make sure the idle switch on the TB clicks when you have it in your hands.
Also inspect the black plastic air hose that connects from the air mass meter to the throttle body for holes. I just had to replace this in my 86. $14 from www.fcpgroton.com
Vacuum leaks like that will cause a whole bunch of problems.
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Rob Bareiss, New London CT ::: '86 244DL- 215K, 87 244DL- 230K, 88 744GLE- 198K, 91 244 180K

My '89 240 had similar problems a couple of years back. I started the car up (while the ambient temp was around 60 or 70), put my car (automatic) into Reverse and it stalled. It got to a point where it finally started stalling at traffic lights. The culprit turned out to be my air mass meter (AMM).

If your car stalls on you on a regular basis, while the car is OFF, try disconnecting the connector to the AMM (it will take you less than a minute), start it up and try shifting it into reverse -- go backwards, then shift into drive, roll forward, then shift into park. If the car runs better without the AMM plugged in, it is most likely the culprit. You could also look around for vacuum leaks. Examine the larger black (accordion-style) plastic hose that goes from the AMM to the intake.

Just be sure to disconnect/reconnect the AMM while the car is OFF. To remove the connection, squeeze the metal pin on the connector and pull up. The AMM is located on the driver's side between the intake manifold and the air filter box -- it's connected to a small black hose that runs from the air filter box towards the firewall. If the AMM is to blame, I recommend changing out the thermostat in the airbox. Long story short, when the thermostat fails, it likes to send hot air to the AMM -- causing premature failure.

Keep us posted.
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Regards,
Eric Staufer,
'89 244DL 119k
My 240 Page