88 burb with problems

[Krosati]

Cool new board, I believe I will be spending a lot of time here now.
My burb has a massive exhaust leak from the right manifold. Cracked all the way around. I plan to replace it tomorrow, but here's the deal.
Most mornings after startup, When I take off from a stop light the engine all of a sudden runs rough as if the timing has jumped. The SES light comes on and all performance is lost. I check the code, its a 43 (ESC). I turn off the truck, to reset the code and continue off to work. I checked the code again and all I get is 12. My book tells me it may be the spark knock sensor but to test it, they recommend tapping the block near the sensor. Would the exhaust leak trip the sensor and cause it to retard the timing? Why would I not have the code stored in the ECM until 50 restarts?
How do I check the static timing on this engine, I know I have to disconnect something and check it at around 500-600 rpm.
Any ideas?