94 S10 Blazer

I am working on an 94 S10 Blazer 4.3 Vortec with an idle fluctuation problem. Just sitting at idle in park the idle will rev up to approx. 800rpm or above. Scanned vehicle there are no codes stored. Watching scan tool IAC numbers will increase as engine speed does. Also when cold engine has no power. Customer seems to think it does this worse when damp. You can feel vehicle reving up while you drive as you come to a stop. Any help will be greatly appreciated.

I am working on an 94 S10 Blazer 4.3 Vortec with an idle fluctuation problem. Just sitting at idle in park the idle will rev up to approx. 800rpm or above. Scanned vehicle there are no codes stored. Watching scan tool IAC numbers will increase as engine speed does. Also when cold engine has no power. Customer seems to think it does this worse when damp. You can feel vehicle reving up while you drive as you come to a stop. Any help will be greatly appreciated.

Check for vacumn leaks and clean TBI butterflys and IAC valve.
And plug PCV valve to see if any difference.

Thanks for help. I cleaned IAC and problem hasnt occurred yet. I still am concerned about low power at times, like low fuel pressure or restricted exhaust.

Thanks for help. I cleaned IAC and problem hasnt occurred yet. I still am concerned about low power at times, like low fuel pressure or restricted exhaust.

For restricted exhaust put a vacumn gauge on it and check vacumn at idle and at 2K rpm.
If vacumn drops down unde idle vacumn at 2K RPM the exhaust is restricted.

You need to put a fuel pressure gauge on it to test fuel pressure for up to specs.

Post back how it goes.

Big or little S-10 Blazer and what engine?