So quick question, this is really starting to bug me, when I am driving home from work and my ac is on and I come to a stop light my idle jumps a little and the drops to around 500rpms and the kicks back up to normal. It only does this with the ac on, with the ac off its fine. Its still barely hitting the 90's so its alright to drive it with the ac off and windows down for now but I need to get this resolved soon.

Plugs were just changed, CAI is on snug, TB is clean, no leaks on the new TB, no vacuume leaks that I can hear or see (although there is a high whistling sound above 75mph only but it sounds like its coming from the CAI), no exhaust leaks, oil has been changed recently, no CEL's or DTC's, WOT A/F is dead on at 12.4, its not running rich, idles at or around 14.7 A/F, adding a can of seafoam or fuel injector cleaner seems to make it stop for that tank of gas.

It was also doing this last year towards the end of the summer but I failed to look into it further over the winter (out of site out of mind type thing). So anyone have any ideas.

 

Well when the AC compressor cycles on a signal should be sent from the compressor/climate control module to the Ecm in order to boost the idle rpm up approximately 100 rpm. What I think is happening is your Ecm is not getting this signal and the fluctuations in your rpm are magnified due to running in a standard low rpm state while additional load from the compressor is applied. Its a long shot but I think this could be whats up. BTW with AC off my truck idles at 500 to 550 rpm all the time.

 

Mine has been adjusted for my mods, it idles with ac off around 700rpms, with the ac on it ups to around 750rpms

 

@Edit
Never mind.

 

Its dropping to the point that its almost stalling out though

 

How do these trucks maintain idle is there an idle air control valve. I know vehicle act weird if these little guys get gummed up. Could we be looking at an EGR problem maybe.

 

well truck here is my two cents,thanks again for the nom, This is a classic case of too much load and the motor not adjusting. I think post #2 is not as long a shot as you think.He may be dead on. That said have you noticed your e-fan turn on when you move the heater control **** too the left?Without touching the ac button. Mine does btw

 

No e-fan. Egr was replaced about 6 months ago

 

Truckin,
Do a search on "Idle Air Control" (IAC) in your manual. Basically when your AC is turned on the PCM is getting inputs that control injector width, timing and IAC. Could be something as simple as a dirty contact on your AC switch. I would try to identify the inputs and check them. My guess is the PCM is not getting the input that the AC is turned on and the idle is fluctuating with the load. Good luck..

 

It's a Hemi. There is no IAC. The drive by wire TB controls idle speed. Better get another book Your TB is not old enough to be dirty already is it?