1995 Blazer 4.3 Vortec Aluminum plenum motor rough idle
 

My Blazer when your 1st start it after it seating overnight it runs very rough and at like 600 rpm and a few seconds running like that it clears up and idles smooth but the high idle never happens its supposed to rev to like 1500 rpm then slowly drop to 800 and it never does that it runs rough for a few seconds at 600 rpm then when it smooths out it idles at 900 rpm and stays there for a while then drops to normal idle. what would make it not high idle anymore its been doing this for months now.

Have you removed and cleaned the IAC and the throttle body throat? Both get full of carbon. Also check that the EGR valve does not have a chunk of carbon that is keeping it open when it should not be.

The '95's have alot of quirks about them.

Low cold idle can be a few things:

Dirty throttle body, have you cleaned it?

Broken Idle Air Control (IAC) valve or wiring

Failing Engine Coolant Temperature sensor (ECT)

Defect TPS sensor

Do you have a scanner? Any codes?

George

Mine is the obd1.5 with the obd2 computer but a obd2 scanner wont scan it even tho it has the right plug any ways it only does this rough idle and smells like raw fuel at the exhaust when it is idling rough like this after it seating overnight then it clears up and idles fine besides the high idle it never does that. I am going to go clean the iac and see if that helps first, also when it does the rough idle sometimes I'll press the gas pedal to rev it to 1300 rpm and let off to see if that helped it run smooth but it didnt and the rpm stayed at 1200rpm and very slowly dropped to 800 rpm like the gas pedal is sticking but it isnt