A few months ago, after a few days of rain, the van started up but then started running rougher and rougher until it just stalled out.   I poked for awhile but ended up calling a tow truck.  The van started up fine when it got to the mechanics.  It was fine ever since.   This morning it started doing the same thing so I pulled over and let it rest a few minutes.  It started up and ran fine again until about half way to work then it started bucking and hesitating.  I made it tow work but what are some things to look for. The bucking does not go away if I just turn the engine off and restart.

1983.5 Westy.

Thanks,
Bryan