1995 Blazer very very rough idle and stalling
 

i have a 95 blazer 4.3L cpi, the engine was replaced around 4k miles ago, for the last few months ive have a very rough idle and and stalling, it wants to stall then surge and drop down again at idle and accleration and decleration, during the drive it is smooth and pleasent, i have not had any codes untill just lately i had a mechanic scan it and it read knock sensor circut failure, the SES light somtimes is on, sometimes is not, in the last 4k miles i have replaced plugs+wires, new battery, new AIC Valve, cleaned the egr, and in the process of replacing the exhaust, could this bad knock sensor be causing my rough idle and time to time stalling/surging, also on a cold start theres a funny squeeky noise under the hood in the engine, could this be traced to the sensor?

anyone have any ideas?

TONS of posts about this issue on the CPI engines. Test your fuel pressure and then watch the leak down rate. Fuel pressure should be >55psi and should only drop a few psi after the pump shuts off.