1998 s70glt runs fine most of the time but stalls sometimes just replaced the vacuum system hoses and canister and plugs could it be the mass air sensor?

Usually, when the MAF fails you will get irradic idle. If it stalls close to home, pull the spark plugs and see if they are dirty. A clogged PCV can cause rich running and fouled plugs.
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My back feels better when I sit in a Volvo seat

I just replaced the pcv system with the kit from fcp groton and we replaced the spark plug at the same time so my plugs are fresh. However, the old plugs were fouled like you said they might be.How about the ignition switch, or the lock button on the underside of the shift lever. I heard from a friend that it could be a bad alternator not supplying enough voltage. The headlights do get brighter when the rpms go up ? is that possible?

Not the ignition switch or the lock button. Most autoparts stores will be happy to check your alternator output, perhaps it is time for new brushes/voltage regulator.

Most cars of that age have developed cracked elbows around the intake manifold. Because your removed all of them and put them back on, check the fitting of the lines and also the air supply to the throttle body to make sure it is tight. Any air leakage will add unmetered air into the manifold, reduce the vacuum level, and make the engine run richer.

Your single coil runs at 12V.
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My back feels better when I sit in a Volvo seat

Thanks Klaus , I will check all those things out this weekend. Awesome advice from the original BB Volvo Ace. I will post the results next week. Thanks again, Pigeon a.k.a. Alan from Salem Va. My butt feels better when I sit in a heated Volvo seat