Hi, my 91 v6 mpi does not like it when i start to break it hard, or even let up off the gas after going about 60, the rpm dips below 500 and such and eventually if i don't put it in neutral and rev it, it dies. possibly a vacuum problem?

 

Possible its a vacuum leak, check all hoses especially the one to the map sensor. I would also clean the throttle body and iac valve. If the iac valve is dirty when you let up off the gas or hit the brakes hard the throttle body butterfly slams shut and the iac cant react quick enough. Is check engine light on?

 

A couple of other possiblilties are:

1) A bad electrical connection (like a ground strap) that normally makes contact, but then opens with the g force of braking.

2) I had a car that did this, and it turned out the distributor reluctor was rusted. Same principle, though. Braking made everything shift just enough to make it stall. The part looks like this: http://eaccess.smpcorp.com/eCatalogs...30&Part=LX-373