I have a 1993 Silverado with the 5.7L 350 with 218,000 miles. I am about at the end of my rope on what to do. I can drive it down the road and it will runs and idles fine. If I let it set for a couple of hours and get it in to come home, it runs and idles like crap. When idling it will sputter and sometime idle down almost to the point of going dead and then surge up. It will do this several times. Sometimes it will go dead. It seems like I can let it idle for 15- 20 minutes and it will eventually quit doing it. I am looking for more stuff to try at this point. Any suggestions are welcome. This all started a few years back and then I could run it today and it would be a week before I could use it again and it run right. Then it finally just quit running right at all. The fuel pump and regulator fixed a lot of that problem. I have a friend with the same model truck with over 300,000 miles on it doing nearly the same thing.

Here is a list of things I have done:

Throttle body cleaning and gaskets
Idle air control valve and the 4 wire harness
EGR Valve
Engine coolant temp sensor and harness
Engine temp sensor
Oxygen sensor
Fuel pump, filter, pressure regulator
Fuel Injectors
Spark plugs and wires
Battery
Checked for vacuum leaks by spraying wd40 around the hoses, no change up or down on the idle when doing that.

The MAP, Mass airflow sensor, rotary button, and distributor cap was replaced a few years ago but I am not ruling them out.

Thanks for your help.

 

Doesnt make sense,after it sits ?,but ok,try suckin air thru gas cap,if it doesnt vent air this would strain fuel pump or u could replace it,not expensive,check throttle position sensor. hope this helps

 

Here is an example. I went to the church which is ~1/2 mile from the house. I worked there for a few hours and got back in it to come home and it didnt want to run right. No it doesnt make sense at all. I will replace the gas cap. It also seems to idle ok sometimes after running it but if I give it a little gas and get it up around 1000 to 1500 rpm it spits and sputters. I can feel it doing that sometimes while driving too but it will catch up. My uncle also checked the timing and he said it was just a touch high but not much at all.