Hey guys my 96 blaz runs for the most part good for 236k one new issue is when its warmed up the a/c on at a stop it starts to idle erratic like it wants to die. I cleaned the maf sensor and replaced the iac still same issue no problems with a/c off. I noticed the new iac control when I first start it up it goes to 1k rpm holds for 45 secs or so then seems to operate fine. I do believe the old iac was bad as the new one when I turn the a/c on the idle does raise a few hundred rpms its ok in park but in idle after a bit it starts to jump around bad.

Any help thanks guys.

 

Hmmm.. seems to me there's a mismatch in the IAC control range.. UNLESS your compressor is having a hard time and drawing too much engine power. It should be pretty noisy if that is the case
Here's how to troubleshoot it, as I did on a ford, not blazer but systems work the same.

Warm the engine up. Disconnect the MAF. Disconnect IAC plug, Remove intake tube from throttle body, clean around and duct tape over IAC port your side of throttle plate.
Start engine. In Park
Should idle between 500-600 rpm, may vary but should keep running and below 650 rpm.

DO NOT Adjust idle stop screw yet! Or EVER until you are sure there is no vacuum and /or fuel pressure regulator leak.

Turn on AC. What happens .. if rpm was about 600 and engine kills, then good chance bad compressor or contamination in system.
Stop engine remove accessory belt. Start engine then turn ac on. If much rpm difference when clutch engages then electrical fault somewhere. Probably NOT a short.. or clutch fuse would blow; bad ground, poor connection that affects engine sensors / controls

Please dont shortcut this.. do exactly as. If I left out something please tell me but if you dont do all that, you cant be sure of the next steps

 

Thanks for the reply back. I did what you said with the sensors also I cleaned the connections and looked for grounds removed and cleaned them. I drove it around was running great then before I got home it started acting up again. I goofed around with it at the house then the check engine light came on. Code po306 and it was misfire in #6 cyclinder.
The plugs are newer ngk's I changed the plug wire I will let you know if it fixed it if not I will put an a/c delco in there see if thats it.