89 z51 wont idle etc

[Corbusa]

I hope someone can help me with this one. My 89 usually idles a little high . but yesterday it was perfect . I stopped for some lunch , came out and she wouldnt idle and was stalling. .I finally got her running and idling smooth , them when I pulled in the garage she did it again and this time it sounded like spark knock. and wouldnt idle.. She has 39k miles , ... Not sure if the injectors have been changed or filter . ( can I tell if they are factory injectors by looking? any Ideas on the idling issue ? a while back I bought an Innova 3140 I guess its time to learn to use it.. Thanks