So I just replaced the alternator, and when I started her up she started and idled fine, but after a few minutes I revved her up to about 3.5k for a few seconds then let off the gas. When I let off of it the rpms dropped down past the idle and tried to die. All of my lights dimmed and it felt rough, but then the rpms went back to normal. help?

 

Sounds normal - Your engine management computer has to relearn parameters

 

Mine did the same thing just a couple wks ago, and I had just replaced my alternator and battery at the same time. After a good three or four days, once things got reset I guess u would say, it was fine. so dont go replacing ne thing for a minute LOL give it time to accept its new transplanted part

 

I agree with everyone else, I don't think it really is a problem as it can happen even to well running vehicles.

If you really feel the need to do something about it, you could clean the throttle body including the IAC bore & valve. A dirty IAC valve can stick and not allow the truck to return to the proper idle setting fast enough which could cause the engine to almost stall when coming down from elevated RPMs.

 

Thanks guys I really appreciate the help, she hasn't died on me yet. However, it now wants to idle at 500 rpms, and is really slow to accelrate almost like it doesn't want the gas.

 

Aha! That is a related problem! Remove your idle air control and clean it. If it started that right afterward, it jammed shut. Intake or choke cleaner, but for the latter be careful not to get it in the electrical part.
BTW: also buy some MAF cleaner and do it as well.

 

lemme ask .... ould you say its ok to spin the little screw on the throttle body to hold a slightly higher idle... my neighbor did it in my truck because it was stalling at idle and he said its a good way to hide booboos lol... but i rolled it back down and now im feelin a rocky idle again.. should i tweak it back up?

 

It needs to be set back to where the factory put it for several reasons.. not the least of which is shift timing.
But after the truck is otherwise running right.

 

Thanks for the help and I will get back with the results. Back on the alternator side though, my headlights are still really dim, and the odometer and gear panel still sorta pulsate when the radio is on or I am at a stop. Do I just need to give it more time?

 

... pulsate and dim is not normal - is that alternator You got rebuilt or aftermarket ? You need to pull it and have it tested to verify 14 volt regulated output .