For non fuel injected models, on the side of the carburetor there is an idle screw. Turning the screw slightly will raise the idle on your Chevy truck.
vacuum leak?
1990 gmc p/u 5.7 wont idle showing code 12
check the ait. on yhe left side of carb..it control's idle.
it has a low idle. Can also be a vacuum hose leak.
Separation of the ethanol due to water in the gasoline.
It depends on the year. If you can't get the idle down, check for vacuum leaks. That seems to be a primary cause of high idle, especially for the TBI engines.
1500 at first until it kicks down to 850 rpm
It could be the Idle Air Control (Idle speed control) valve. Its located on the left side of your TBI and has an electrical connection.
A 95 does not have a idle air tempture sensor, It was not used on that year, no need for one.
While the truck is running in idle pull out the dip stick and read it.
It shouldn't need reseting? Probably controlled by the PCU (Computer)