2000 toyota avalon xl keeps stalling

[biotech]

i have a 2000 toyota avalon xl. the car starts and stalls, episodically and unpredictably. it is serviced regularly, has @84,000 miles and has had to be towed twice in the past two months. the service centers can’t seem to isolate the problem, because when they get the car, it starts. my husband hit the intake manifold with a deadblow hammer and it started. any ideas? thank you.