Ok, when i come up to a redlight, and sit for a couple seconds, the idle drops from 750 or whatever its suppose to be at....to 500, then jumps back up...so when your sitting there, the truck will jump....My friend thinks its something with the heater because if its on...it will do it like 2 times per stop light...but if its off it doesnt do it....i did just put a system in a couple days ago, and it started after that i think, but the battery meter is fine...even when i turn the subs up it doesnt move....so i have no clue what it is, but its annoying as hell...

Rocky

 

To start, check your MAF sensor, might need some cleaning. Throttle body would be next, and air filter should be an obvious check.

If it's purely electrical, check your battery for proper fluid levels, and/or charging. Both can be done for free at your local autozone, because they'll love to sell you a replacement.

 

I hate to say this cause I love my Fords, but honestly, for me, its been a Ford thing. Happened to my Mystique I had, then to my Mustang. I wouldn't be afraid to say that it could be an EGR valve going or an O2 sensor. Depending if you have that stuff hooked up. I would think the EGR would cause the motor to rev higher, but the O2 sensor causes the bad idle. Mine started like that and a few thousand miles later I got the check engine light on. Im not saying im right, but its a thought if you are driving yourself crazy trying to find a fix.

 

I have had 3 rangers with a/c and when its on defrost or bi-level it will jump slightly because the ac compressor is cyclying, i just turn the **** on vent only and it dont do it.
my 2 cents.