1988 Volkswagen Van

I have an 88 Volkswagen Vanagon. When I last drove it it was bogging down and bucking as it was going down the road especially when it was cold. The conclusion that my mechanic husband came to was that it needed a mass airflow meter. We let the vehicle sit for about a year starting it just a few times, as I had another car to drive. Three weeks ago he installed the new airflow meter and the van will not stay running. It stars and then the RPM needle goes to 0. If you continue to give it gas you can almost keep it going. Popping and backfiring. We've also put a bottle of dry gas and a bottle of injector cleaner in to no avail. Any input you could give would be appreciated.