I have a 99 f150 w/ 4.2l. The truck was running great the other day. Went to lunch and it ran fine. Four hours later I start it up and by the time I walk to the truck (remote start) it was idling really funny almost like it had a very bad miss nearly to the point of where it would die out and then it would rev back up. This usually happens if I let it idle for about 5 mintues. Never could figure out the problem. Anyways, I drive off and give it gas and it sputters some for the next mile or 2 and it was reasonably cold out so I thought ok maybe it needed to warm up and sure enough it stopped doing it.

Now whenever I get on it and hit around 3-3.5k rpm it starts to sputter real bad and jerk around. Once I let off the gas it is fine. On other occasions I can get on it and itll rev right up to 4.5k-5k and shift. Then when it shifts and goes back down to 3-3.5k range itll start to sputter real bad again like it wants to die out pretty much and stops picking up speed. I thought ok maybe its the transmission being that it only happens in a certian rpm range BUT I can obviously hear the engine spitting and sputtering actling like it wants to die out.

Does anyone have any idea as to what the problem could be? Im thinking wires/plugs or dirty MAF? Although the plugs only have about 20k on them and the wires maybe 30k. The air filter has also been cleaned.

 

You might try scanning for codes. Even if the check engine light isn't lit, it still may have a code stored.

 

This sounds like a vacuum leak or it's starving for fuel.


The rest of it sort of sounds like a misfire. Definitely have it scanned. You should at least have a pending code or something, and that's the best way to know where to look.

 

It has always had the codes that read "bank one lean" and "bank two lean" changed the o2 sensors and that wasnt the problem so it seemed like a vaccum leak. Never could find it though and the truck still ran fine. This weekend im gonna change the plugs/wires and if that doesnt fix things its off to ford. With my schedule I dont have the time to fool with it a whole lot.

 

Since you don't have too much time, try this quick fix:

Try cleaning your MAF sensor before you do anything else. Disconnect your battery while you're doing it and leave it disconnected for 20 minutes or so.

If that doesn't fix it, you most likely have a vacuum leak.

 

I definetly will have to do that saturday when I change the oil and check the plugs its been about 5-6k miles since ive cleaned the maf.

 

my money is on a vacume leak as well...I just went through a simalar issue with my 5.4 in my 97 150.