I just bought a 91 honda accord se and when you go to stop it stalls or suts off. any ideas of what may be causing this

Check your 91 Accord's ignition coil. The coil goes bad at apprx. 150k miles and cause the car to run rough, hard to start(long cranking time) in the morning, stall after the vehicle has warmed up, cut out while driving and backfire horribly when accelerating from a standstill.

Weak fuel pump?

I have had similar issues with my 1982 Chev half ton over the many years I have owned it (since 1983). There are many possibilities and many of them were caused by minor issues like vacuum leak, fouled plugs or poor spark, timing, fuel filter or even air filter. As you probably know, many of these items are easy to check without spending alot of money. When the engine is reving at higher RPMs the problem seems to go away but at lower RPM's, like when you are comming to a stop, it stalls out. If you have a tachometer you can check to see if the idle speed is correct. If it is too low, this may also cause it to stall. This would happen more often in colder temperatures and I would sometimes increase my idle speed in very cold temperatures. Not sure what type of setup your vehicle has for high idle during the warmup period, but if your vehicle is not warming up properly caused by incorrect high idle setting, this may also be an issue. If it still stalls after the vehicle has been warmed up, you could probably strike this off the list. If it runs really rough before stalling out, this may be caused by the other items listed. I would start with checking the idle speed in park and in drive, confirming how well he engine is running, and start troubleshooting from there. Hope this helps.