idle surge

[97sprt4x4]

So I've been having a problem with my idle, and i'm unsure what is the exact problem. When my truck sits and idles, it will be idling fine, and then you will hear the fan click on and the rpms will drop 2-300 rpms to around 500 rpms and get really rough. then the truck will rebound and idle fine, and then it will do it again a few seconds later. It's kind of irritating because if i have anything running the lights will dim and i'm afraid to put any sort of sound system in until i figure out what is wrong. The plugs are brand new, but i have yet to change the wires or coil pack. where should i start with this problem??

 

[robertoa1a]

It could be a slightly low battery. Check that first.

When the fan kicks on, (as you have explained) that is most likely the A/C pump cyleicing for an unexplained reason.

Can you elaborate a little?

 

[dogfriend]

You might have a bad IAC. The IAC (idle air control) is supposed to maintain the same idle speed by letting in more air when the A/C compressor kicks on. If the idle bogs down when you shift from P into R or D, that is another sign that the IAC isn't working right.

 

[97sprt4x4]

Well when I put it into drive the Rpms drop to around 5-600 but they stay there until I release the brake. Would I be able to clean it with sesor cleaner or will I have to purchase a new one for it to correct itself?

 

[dogfriend]

You can try cleaning it to see if that helps. If you search on IAC or IAC cleaning, you should get a lot of info, it is a common problem.

BTW, idle speed in P or N with a warm engine is supposed to be 750 -830 rpm.