I have a 05 F150 4.6 liter with 107,000 miles.
I just replaced the alternator and that fixed my electrical problem but afterwards my truck was not running right. It dies at stops lights or when I slow down. When it does idle at stops, it isn't fluid. The RPMS bounce from 1500 to 500 as if I'm lightly pumping the accelerator. I changed the fuel filter 3 months ago. I just started doing my own minor maintanence so excuse me if the problem is obvious. Please help!
Thanks in advance for any advice!

I forgot to mention my check engine light is on.

Also, I found others on a different site with the same problem and they suggested to follow the procedures in the
owners manual under battery replacement. Disconnect the battery, start, let idle 10 min., turn on AC and let idle for a few more
minutes, then drive for about 10 mile. This is supposed to let the computer relearn proper idling.
Guess I will try this next.

 

The check engine light means that you have codes. Take it to someone that has a reader and have them read. Some of the automotive parts stores will read them at no charge. Post the codes here some of the good folks will help talk you through the issues.

 

ya man, youre lucky enough to have a CEL and haven't checked it out yet?? cmon, youre shooting in the dark without checking what the code is saying.

 

Damn the luck, I hopped in my truck to go to the auto parts store and the check engine light isn't on anymore. But of course the idle problem is still there.

 

I just bought my 05 lariat and when i signed it out on a 3 day waiver it had the same stalling poblem.

the dealer fixed it and i continued test driving.

they replaced the throttle body and the truck ran perfect.

hope it helps... sorry if im too late

 

The check engine light may no longer be lit, but there could be pending codes that will help you out. Not to mention that you may have the light lit by the time you get there.

 

could possably be coil issues

 

Remove The plastic Air cleaner tub And open the throttle body Butter fly Look in behind With flash light If it is drity And it will be Remove throttle body the And clean with some degreaser 4 bolts and two elec plugs be care full with gasket if not damged reuse worked for me

 

Reset comp buy removeing Ground cable off of battery for the time it takes to clean the throttle body about 15 min

 

I went ahead and bought a code reader but there were 0 diagnostic codes and too many pending codes to determine anything. I'll check out the throttle body. Thanks for all of the suggestions.

 

CEl came back on so hooked up the code reader and got a P0506 Idle Control System-Low RPM. Base on my research I'm thinking it is the idle air control valve.

 

Check to be sure you don't have a vacuum leak in the hose running from the PCV valve to the intake. They are notorious for deteriorating and the up/down idle sounds liek a vacuum leak to me.

 

You have a fly by wire throttle system. No Idle air motor. Try cleaningthe MAF sensor. Could also be a bad Throttle body motor.

 

Last night I decided to clean the throttle body and clean the MAF sensor at the same time. This morning on the way to work, truck idled great! It's very rewarding fixing your own truck, not to mention less expensive. I just started changing my own oil a few months ago.

Thanks for everyones advice!