Fluctuating idle when heater/AC is on

[SkagitBoy]

Hopefully somebody can help with this issue. When I’m in park or in gear and stopped, if I turn on the heater the rpm’s go up and down between 700 and 1200 rpm’s or so. However, it doesn’t do it if I turn the heater to defrost.
It’s a 96 XLT 4.0 AT 4x4. I’ve cleaned the IAC and MAF. The IAC was very dirty… cleaning it didn’t seem to do anything.

Any suggestions? Any help would be appreciated!
Thank you

 

[franklin2]

See if you can find the vacuum line that supplies the HVAC system. It usually goes to the pass side to a vacuum storage reservoir, and then from there goes into the interior through the firewall somewhere. If you have a problem somewhere in this system, it may create a vacuum leak to the engine.

If you can find it, pinch it off or plug it somehow, and see if the problem goes away. If not, then you can look for the problem somewhere else. If it does affect the problem, you can then investigate the HVAC system and see if you have a vacuum leak somewhere. While you have the vacuum line plugged or pinched off, some of your HVAC dash controls will not work.

 

[SkagitBoy]

See if you can find the vacuum line that supplies the HVAC system. It usually goes to the pass side to a vacuum storage reservoir, and then from there goes into the interior through the firewall somewhere. If you have a problem somewhere in this system, it may create a vacuum leak to the engine.

If you can find it, pinch it off or plug it somehow, and see if the problem goes away. If not, then you can look for the problem somewhere else. If it does affect the problem, you can then investigate the HVAC system and see if you have a vacuum leak somewhere. While you have the vacuum line plugged or pinched off, some of your HVAC dash controls will not work.

Thank you, I will try that today… appreciate your help.