engine dies while pulling codes

[Devin Avery]

I am having a strange problem while trying to pull the fault codes for
my car(88' 90q).  After I insert & remove the fuse in the fuel pump
relay for the first four seconds my car dies.  I get the code 2312
(coolant temp sens.)after doing that.  I also got this code a while back
before this started happening.  The car also seems very flat over 3500
rpm. I plan on replacing the temp sens in the very near future and going
from their, but any BTDT or suggestions would greatly be appreciated.

TIA,

Devin Avery