rpm's rev up every 8 seconds

[TweakedGM]

I have a 1996 gmc 5.7L auto at an idle the truck starts to rev up from 750 to 1000 rpm's every 8 seconds. winter is coming along and I don't need the tires to break loose and spin on snow at a light. Its not misfiring runs perfect.

[ebedsilva]

I would have to say a very small vacuum leak. My uncle's ford did the same thing and it was a tiny hole in a line. replaced it and fixed the problem. Also, you can reset the computer and see if its electrical related.

[TweakedGM]

Changed idler now the rpm's stay level. I believe idler was starting to cease which brought the rpm's down and the comp took it back up.