Before consenting to replacement of any expensive parts like airflow meters or throttle modules, I would look carefully for an air leak anywhere in the intake system. If a vacuum hose has a crack it may be letting in air under some conditions and not others. This would include the flexible hose from the air cleaner to the throttle body.

I once had such a behavior (not on a Volvo) which turned out to be a cut in the power brake vacuum hose. Sometimes it worked and sometimes not, depending on the flexure of the hose.

Did you get a "check engine" light?