Chevrolet Repair: Electronic spark control circuit, astro awd, minimal info

Question
Started hard starting about two weeks ago but would eventually fire up. Just replaced the plugs, wires, rotor, cap & fuel filter. Yesterday! Still, cranks and sputters abit but no fire. Pulled the code 43 Elect. spark control circuit. And then became clueless.
My chiltons only gives minimal info on this particular code. HELP! I Hate going to the dealer when it's something I can fix myself. What do I do?
93 astro AWD  4.3L  Thank you Mr. Expert

Answer
Hi Kelly,
I seem to show that code as "43 Knock sensor signal was either above 3.5 volts or below 1.5 volts for at least 20 seconds.

Possibly EST caused. Dirty injectors??

Check this chart, and see if it helps you any.

http://www.troublecodes.net/GM/

Van