i had this question back along last year when i first got my idi.
i explained while asking,that it shut down like when the older(pre ob1/2) gas engines timing was off with the shake you describe.
was told it was normal.
after a couple months i didn't notice it doing this anymore.
i recently got a timing meter for my diesel,and advanced the timing 2.5 degree's.
my engine now has the "improper gas timing shutdown" to it again with correct idi diesel timing.
i thought this was very interesting.just thought id share my new found experience with the idi and add to the bucket of confirmations of "all systems go".