The stalling fixed itself. On a test run to Lewisburg and the bank, the van coughed and stumbled into the drive-in line, idled fine for the several minutes it took to make a deposit, then I took off for home, ready to catch the engine at every stop. No problem at all, the rpm dropped but held at about 800 - 1000 for every stop. So I've put away the problem, but am pondering what could fix itself in this scenario.
My hypothesis originates with experience with our V70, which also has a MAF. For years, it was occasionally stalling at stops. Complaints to the dealer were useless, since it would never stall while they had the car, and there were no error codes in the computer. However, as part of the Great Power Steering Pump Debacle, we had taken it to AutoScandia in Herndon, Virginia, and it coughed on them while they were test driving it. The technician said this indicated that the MAF needed to be cleaned, and did so. It's never stalled since.
As almost everyone who does this conversion will probably do, I purchased a used MAF. It did not come in a plastic bag; on the contrary, it was pretty dusty. A MAF error could cause this stalling, and the MAF can conceivably clean itself . I don't have information on this particular unit, but the platinum-wire MAFs used in the Volvo 240 series would heat the wire briefly after the engine shut off, to burn off any contaminants.
I plan to run an Elmscan log of the MAF output, the throttle position, and the fuel trims before and after a MAF cleaning, and see if there's an obvious difference. In general, though, I think that anyone buying a used MAF would be well advised to also get a can of cleaner (about $6) and follow the cleaning directions, which would be easy to do before installing the MAF. Another thing I wonder about is the possibility of plastic dust in the airbox from the modification process. I washed the box after I was done modifying it, but there's always the chance I missed something on the "clean" side of the air path.
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