Mass airflow sensor?
 

I have a '99 Silverado 5.3, just over 100k miles(25k when got it). Never had any mechanical issues. It idles at 200rpms for maybe 10 seconds then dies. If I touch the gas it dies. Initial codes showed mass airflow sensor, O2 sensor, system lean. Have replaced the sensor 3 times(3rd on off chance I happed to be so unlucky to buy 2 bad sensors). After replacing and clearing codes I got no change, but new code for throttle position sensor, replaced it, no change. Have removed/disconnected O2 sensors and retested, no change. When I unplug the mass air sensor it idles and runs fine until it warms up, then sputters and dies. Have also replaced fuel filter and plugs. Going to try coolant temp sensor today. Any suggestions or ideas?

Have now replaced coolant temp sensor, no change. Also verified fuel pressure.

The MAF won't keep it from running. There have been issues with the coolant sensor screwing with the TPS. O2 sensors are just for emissions. Have you done anything to the throttle air plenum? I'd revisit the TPS I delt recently with mine just dying with maf sensor off performance as the only code. That was because the engine just died, this turn out to be the ecm.

Haven't done anything with air plenum. I read in another thread about a security feature on the ignition switch that shuts off the fuel if its tampered with. Recently I started having issues with the key not wanting to turn. Can anyone verify for me if the '99 has this feature? As its a dealer only repair.

I'm not sure what security system you have, what does the ignition key look like?

Standard key. No battery or chip or anything in it

Are you getting a security light on start attempt? If it's passlock 2 it won't start, but will crank.

I haven't checked this yet. The security light would have been on though as it comes on if the key is turned and driver door open. Will check tomorrow