Your problem is fairly common with the LH 2.2 system used in your '85 DL and is very likely related to maintenance of the idle control system. In addition to cleaning your IAC valve as suggested by Gene, I would also clean the throttle body (remove to bench for a thorough cleaning) and your PCV system (the flametrap and especially the small vacuum hose from the flame trap). You should then verify the operation of the TPS (throttle position sensor) switch -it should click just as the throttle starts to open and click again just before the throttle reaches the rest position. You then need to check/adjust the base idle -ground the red/white wire in the open test lead (left inner fender) to close the IAC valve and set the base idle to 725 rpm using the big black thumb screw. You can find additional details on all this in the 700/900 FAQ Feature Section plus lots of good stuff in the Archives (use an advanced search).

If the problem continues then suspect a faulty/sticky/worn IAC valve, a problem with the Hall Effect sensor in the distributor and only lastly would I suspect the AMM for this type of problem.
--
Dave -not to be confused with a real expert

Remove and clean you Idle air control valve. Use carb cleaner. This should do the job.

Unplug the air meter. You may be able to "limp" it home. If it does, you need another meter.

May have a failed Air Mass Meter. Best way to check is to substitute a known good unit.