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It seems as if there is an idle problem, accompanied by weak ignition.
The problem could be related to a vacuum leak, idle air control, idle switch, throttle body adjustment, clogged air filter, or about twenty other reasons.
Mostly reverse is where the car will stall, if it has a weak idle. Even if the idle speed is right, it's easy to spin an engine at idle speed with no load.
There is no way that the transmission could be damaged so as to stall the car only in reverse. All power passes through the torque converter in one direction before it hits the gearbox part. No matter if the gearbox was locked solid, the car should stay running because it is just as if the car is sitting still in Drive or Reverse.
However, I belive that some ZF transmissions had a lockup feature on the torque converter. If that malfunctions it could cause the engine to kill. I don't think that the AW70 had a lockup in 1987. It would help to know what transmission you have. The ZF transmission is much more complex with respect to the service and repair procedures, than is the AW70.
If you bring the idle to 1000rpm and put it in reverse, does it still stall immediately? When the car is warm, I mean. As high as 1200 for test purposes, one or two times with AW70 trans only... This will rule out a trans problem, and highlight a slow or weak idle condition. If there is a little play in the driveline, the engagement into "R" can be very harsh. Ditto for drive, but it depends on how you parked the car.
With the ZF transmission, there are numerous faults that could cause either double-engagement of the transmission, harsh engagement, no engagement, etc. The Volvo diagnostic manual has about twice as much information on diagnosing ZF faults as it does on diagnosing the Borg-Warner/Aisin Warner varieties.
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Chris Herbst, in Wisconsin.
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