Went to advanced auto and code P0300 is gone but now is showing code P0118. Coolant oxygen sensor. Ordered a new one going to install it tomorrow. Ill let you know how things go

 

DTC's never tell you to replace a part. They tell you what circuit malfunctioned. Might want to make sure the ECT sensor is plugged in, they may have unplugged it when they replaced the injector assy. Here is a link to the flow chart for P0118:
https://blazerforum.com/forum/diagno...plained-36766/

 

You were right. They did not plug it back in. check engine light is gone. Rpms still seems to shoot up to about 1000 when i crank it and when im stopped they stay at 500..

 

Cool, glad you found it. Thanks for posting back. 1K RPM on start up is normal. When the engine is at operating temp, it should idle ~550 RPM.

 

Haha i feel like an idiot than. thanks for the help man. youve helped out quite a bit.