My truck idles about 900 and is fine with me since it is manual. When I turn the A/C on the idle drops to about 750 and then after 30 seconds or so drops off to about 600 and fluctuates like a non-stop slow bouncing ball between there and 850. The idle is about as smooth as normal with no A/C while it is fluctuating with the A/C on. When I turn the A/C off idle goes to about 1300 and drops back to 900. Timing is correct.

This is not an issue that now effects driving or idling either way with the a/c, it just doesn't seem normal and I would like to fix it if there is a problem. In South Texas we use A/C about 11 months a year. Thanks Sandy

 

First thing I would do is to clean the IAC valve and reset the computer (ie, disconnect the battery for 10 minutes) and let it re-learn the idle.

 

Thank you. The IAC is only 2 months old. Another bit of info. I just drove the truck about 8 miles and when I slowed from freeway traffic to turn it died but started right back up. Yesterday when I first used the a/c it died at a stop sign but started right back up and nothing until today. I can only assume that the idle goes so low when it is fluctuating that it dies.

I have no CEL and I ran a KOEO test and no codes. The only other thing I can think of is the holes in the TB butterfly valves have been closed with JB Weld which was done last week when we (forum) were working on a high rough idle.

Other than the holes being plugged could I have an air leak in the A/C system causing the low fluctuating idle with A/C on?

I am going to reset the PCM now and go drive it again and see if it happens and will check back soon. Sandy

 

check for vacuum leaks, there is a vacuum tank on the side of the heat/condenser housing underneath the foil covering that could potentially be leaking.

Also the white PVC line the runs to the vacuum actuator next to the fender apparently breaks down & is a common source for vacuum leaks.

Do the various AC modes work? I knew I had a leak when it would take forever to switch from defrost to max AC; it also would switch back to defrost under engine load (no vacuum). I also replaced the vacuum check valve that splits vacuum between the AC controls and the HVAC reservoir. Note that the HVAC reservoir is not the same as the "coffee can". It is a plastic container that is sonic-welded to the side of the HVAC assembly in the engine bay.

 

Thanks jas88 and mark 1986. Resetting the PCM did the trick. As I slowed with A/C on I watched the tach and it never dropped below 900. Got home and turned A/C on and off in the driveway and tach stayed the same and idle never fluctuated. Nice easy fix for a change. Thanks again guys. Sandy
Mark, I have been through that vac actuator and it was an issue and already been fixed.