here is my problem. when my 97 f150 5.4l truck is at idle i get a rough idle. almost feels like it wants to die. i have replaced the EGR valve, the Mass Air Flow sensor, the Idle Air Control valve and the DPFE sensor. when i first noticed the problem i had a MAFF code come up, then just yesterday i had a 1401 code (DPFE). About 2 months ago i had the catalytic converters on the drivers side replaced at Meineke. they used two of their universal cats because it was a lot cheaper. before having the cats replaced i had an O2 sensor code but the mechanic said it was probably because i had holes in the cats. so after replacing all these parts i am still getting the rough idle. can anyone please help?

 

Would the roughness go away if you step on the gas just a bit (to rev the engine to about 900 rpms)? Do you get misses and hesitations while driving normally, or the engine runs great EXCEPT for idling?

Let us know, and good luck!

 

I assume your ignition parts are new as well?

You could also idle it for let's say 10 minutes and after letting it cool off pull the spark plugs. The look of the spark plugs could tell you if you have a miss fire on one particular cylinder and many other possibilities.

Did you run a few tanks with fuel system cleaner?

Did you check for vacuum leaks?

From what I gather there were a few parts thrown at it based on the codes. The codes don't replace proper old fashioned diagnostics.

 

cougarfan: yes the roughness would go away if i give it gas. runs great while driving.

Bluewind: just had new splitfire E3 plugs put in it about 4 months ago and i have checked for vacuum leaks, none to be found. today it sounds like the engine is loping, just cleaned the K&N filter thinking it may of had too much oil on it and also cleaned the MAF. guess i am going to run some fuel cleaner through it and see what happends. if you guys can think of anything else please feel free to let me know, otherwise thanks very much for reading and replying.

 

I do not trust the E3 plugs. I am thinking they put up a lot of hype without scientific proof of their claims. I would definitely look at them. Every Haynes manual has color pictures to help with interpretation.
I am not terribly familiar with your engine. The Windstar engine has Intake Manifold Runner Controls that open the short intake runners above 3000 rpm. If they don't close properly they can cause rough idle. There are small plastic grommets on the linkage of the control. These grommets brake and get lost. If your engine has IMRC that's a place to look.
Fuel injected engines have also a cam synchronizer that can go bad.

But honestly I would keep driving rather than throwing parts at it.

 

I'd check for vacuum problems - such leaks are obvious (and annoying) when the engine idles (and diminish or go away when you step on the gas) because the leaked air flow with the throttle plate closed is comparable to what the IAC valve lets in, thus throwing your idle all over the place. But there may very well be other causes I'm not aware of ...

Good luck, and let us know how it goes!

 

Best way to diag this is with a scanner; look at the time-adjusted long term fuel trims for both banks after it enters closed loop (usually only take about a minuet, tops to enter it). If the LNGFT1 and 2 are off by more then 10 percent (either way), you have something to look for (too rich, look at fuel system for correct pressure/delievery; too lean, vacuum leaks).
One other note: I've done driveability for longer then fuel injection has been around, and the O.E. plugs really are the best in most instances; Ford has spent a ton of money designing plugs that promote the best burn characteristics that you can get for the engine, while still keeping within Federal guidlines for misfire tolerances. Just food for thought.]
On the other hand, I remember I couldn't even diagnose a set of bad plugs and wires on Cougar Fan's car, so, take it with a grain of salt. I'm not there!

 

Boy, don't remind me of the bath we took with cougar-fan's car. It was indeed a repeat learning experience. After you get burned enough, you learn, and I agree 100% stick with OEM parts by all means.
There is a lot of hype out there for aftermarket stuff. Not all, but most are poor quality imported junk and a good example of "You get what you pay for" !

 

Dear Greasemark and Hanky: please don't go hard on yourselves, you know your stuff darn well, and your advice here is invaluable. We all got carried away when diagnosing my car's problem , at the end of the day it turned out to be a great learning experience and an exemplary team work. I don't have enough words to thank you two and Hayapower for helping me get to the bottom of that issue. That's why we're here, to think and share our thinking for the benefit of those in need.

Cheers,
cougar_fan

 

Thank you cougar-fan for your kind words. I have , but one problem now, my hat got too small!!
Back to the problem iuecbrad has, We all seem to be in agreement that there is a vacuum leak that is affecting the engine at idle. The problem is to locate it.
I'm not positive that this is a 5.4 engine, could it be a 5.8 ?
There are a couple of ways to try to locate a vacuum leak. Of course the ideal way would be to smoke test it. That equipment may not be available so another method might be to pinch off all the vacuum lines you can find one at a time and see which one if any causes a change in the idle quality. To supplement this you might try spraying carb/choke cleaner to areas you cannot access too easily. If it is a 5.8 there are loads of vacuum lines and hoses to search. This is one of those problems where perseverance pays off. It could be something like a worn throttle shaft on the throttle body. As long as the spray doesn't get close to the intake hose it should help to locate the leak. What do you think guys?
Let's hope it isn't a valve problem.