trouble code 29, crank angle sensor

[briansel]

my '92 svx had been running a little rough and was giving me the check engine light off and on. the problem got worse about a week ago when it started shaking at low rpms, mainly noticeable when starting from a stop and when the tranny shifted into overdrive on the highway. i recently checked my trouble codes and got a 22 (knock sensor 1) and 29 (crank angle sensor 2).
I replaced the spark plugs a few days ago and im going to replace the knock sensor today. id like to replace the crank sensor myself too, but it requires removing the timing belt and a lot of other stuff, so we'll see if im brave enough.
anyway, what im really looking for is some explanation of the role of the crank angle sensor and what could have caused its failure. a new sensor cost me 170 from pep boys (everywhere else was over 300) so i dont want it to fail again for the same reason.
thanks a lot for any help, i dont want to let this one go!