Ok first off my truck got stuck in 4WD and refused to come out even when the switch was moved back to 2WD. Then I now have a recent problem with the engine rev. When the truck is idling like at a traffic light or just when its started and throttling the revs are very irregular. It behaves like its not getting enough fuel and like it wants to shut off. In fact in has shutt of on quit a few occasions. It also will just rev very high and then go below 800rpms. Any ideas??????????

 

I have had this problem on and off at times

 

Could be a vacuum leak, ie the pcv hose elbow behind the throttlebody, or a bad iac valve. Any codes? CEL on? Come on, help us out a little.

Robbie

 

Also check the vacume hoses behind the battery.
With the engine running spray some ether around the vacume lines, if the engine RPM's increase then the leak is in that area.