After I start my truck I notice that the engine kinda jumps from like 600rpm to like 6500rpm........its like a fluctuation of sorts, and I hear a noise coming from under the hood, sounds like the AC kicking on and off. If anyone can tell me how to fix this and/or why its doing it that would be great.

 

is your a/c on or in the defrost or floor defrost mode?

If you are low on refrigerant the a/c clutch will kick in and out more frequently and this will affect your idle. Assuming you meant a 50 rpm change not 5900 (!) rpm.

that I think would be a whole different ball of worms.

 

yeah sorry I meant 650 not 6500, and I do have defrost on most of the time.....so you think refrigerant is the probelem, i will try that tomorrow before work and see if it fixes it.

 

it could also be a lean condition in your engine, or a bad O2 sensor, if it senses a lean condition it will try to equalize it by dumping in more fuel, so it wont go into a "closed loop" idle

 

A simple way to test the theory is to switch your climate control to "panel" or "floor" these settings dont engage the a/c clutch.

My 96 bronco was such a fuel pig that I would pull the wiring plug from the a/c compressor in the winter to save on fuel, but the plug is in such a P.I.T.A. position on my 03 5.4l that i am considering wiring a switch on the dash to interupt power to it. I'm not sure if or how the computer would react to such a modification.

 

"Whitetrucks" ur a/c setup should be the same as mine. i have a 99 5.4, there is a plug on the a/c condensor, if you unplug that your compressor shouldnt kick on and off. thats what i did and i havent heard it yet

 

Also check the simple fix and see if there is anything caught in your air filter and or any fuses blown.

 

sorry about the temporary thread hijack:

Yeah that's kinda what I was thinking but the plug on the bronco was right up on top of the compressor on top of the motor, easy access unlike the '03- 5.4l

I think I may use the G.N.D.N. (goes nowhere, does nothing) switch left on the dash from when my rig was a telephone co. service truck. to make this mod.

I now return you to your regularly scheduled program...