I was driving to work this morning with the A/C on and noticed that the truck was idling weird when I was at the red light: the RPMs would drop and go back up every 4-5 seconds. I have cleaned the IAC in the past (a couple years ago) because I was having a similar issue when I would shift the truck into park, but it didn't solve anything. Would it seem that the IAC has gone bad and needs to be replaced?

 

What size engine ?

 

V6 4L

 

Does it do it with the AC off?

 

It only does it when the ac is on and I also noticed that it doesn't do it as soon as I start the truck. If I drive a little bit and turn the ac on while its idling, it starts idling really rough. Also, if I shift from drive to park, the truck idles so low that it stalls out.

 

That sounds like an IAC. Mine would dip down in rpm every few seconds. I was lucky that a good cleaning did the job.

 

Just curious when was the last time you changed plugs and fuel/air filters?

 

Its been at least over a year on the filters and I don't even know the last time any plugs were replaced.

 

Personally I would start with the basic tune up first then...

 

I had same problems with my 3.0 put on a new IAC and no problems for over a year now. I did notice a little better in town mpg.

 

Might want to try this first:

 

Thank you for the all of the reponses. I'm going to start with the basic maintenance first (replacing the filters and plugs) and then try cleaning the IAC before I replace it. I've cleaned the IAC in the past but it didn't do anything in regards to the stalling issue when I shift to park but I'll give it another shot.

Someone I work with suggested cleaning the throttle body as well, would that be something I'd want to try as well?

 

Maybe not the most popular, but I just unplugged mine and set the idle manually. Works fine A/C or not, all I have to figure out is tricking the CEL to turn off.