I have a '93 5.0 with a new fuel filter and a fuel pump which is 2 yrs. old. Every once in a blue moon and generally when taking off from an idle position or while gearing up it looses power, may die but usually just looses power and won't go over 5mph. Sometimes it clears up immediately other times it has to sit for a while and then it's fine. I could hop in and drive 500 miles and have no problem but it's not reliable. I don't want to pay the dealer big $$$$ if it's something I can fix. I added some Lucas additive to the gas upon advice from a mechanic but it didn't help. Any ideas?

 

I had a problem similar to that in my 88....as far as I can remember there is a sensor over by the intake plenum that you can take apart and clean with carb cleaner....I had a problem with the car staying idle until I cleaned that out, but you might have a different problem....

 

So what I think am getting is that when you are stopped at a light or parked, as soon as you put it in gear it stumbles and/or dies? Also what tranny do you have?
Just to make surethe basics are covered - is everything 'in tune'? Spark plugs, wires, rotor, cap- all in good condition. Make sure all vacuum lines aren't open or not connected to anything. The car is timed right (with timing light).
By the way, for you, how often is 'once in a blue moon?' Is it once a week, month, few months, etc..?

 

Sounds like you might be picking up rust from inside your tank. If you let it sit for awhile and it works fine after that, that would indicate the rust sediments have had time to settle to the bottom of your tank and your fuel has cleared up. As your car begins to move your moving the rust around again. That would cause it to hesitate or even stall once the rust has had time to swirl around enough inside your tank. Has your tank ever been replaced ?

 

Gt you are talking about the Idle Air control valve. That wont cause the car to stumble or die once he takes off. I would try the Fuel pump, could be a loose wire on your pump or you pump could be faulty. Fox is right also could be rust. I my first thought would be fuel pump though. One thing you could do is get a fuel pressure gauage and hook it to your strator vaule on your fuel line and watch you fuel pressure as you drive and drive around till it does it, if it drops when your car messes up I would say that is what it is!!!

 

How about your injectors??? I din't realize how bad mine were until I took one out and it basically fell apart in my hand....