I have a 97 F150 with 5.4 L V-8, 138,000 miles. Started having rough Idle problems about 75 miles ago, and check engine light had been on for several months. Used fuel injector cleaner additive to gas on 2 sucessive times, but didn't help.Code indicated bad O2 sensors, so I put in 4 new Bosch O2 sensors, new air filter and a new fuel filter. Put in different gas from different station,
thought maybe I had bad gas.Still no improvement.
Reset code and check engine light came back on after about 10 miles of driving.
Still having same rough idle problems and code reader says gas / air mixture to lean. I haven't done any tune up to truck in approx. 20k. Any suggestions on what to do or check next???
Thanks,
Don D.

 

Welcome to the forum
I would start by checking the PCV hose elbows. They are known to crack and suck air, especially the one the hooks to the back of the intake manifold.
You might also need to clean the MAF.
There are instructions to cleaning the MAF in the Read First thread at the top of this forum.

 

LxMan1,
Thanks for the suggestion; I will check the hoses and elbows and clean MAF.
Sincerely,
Don D

 

Turns out your idling problem could also be do to a dirty or bad ICV valve. I had a similar issue with this back two summers ago. I took it to a Ford dealership and had them run a diagnostics on it. Turns out (they said) the mass-air flow sensor and ICV valve needed to be replaced and it was going to cost me about $1300 with labor included to get it repaired. Very much sckeptical about this, I said thank you very much but no and paid for the Diagnostic test ($75), and proceeded to as for the code print outs. They obliged, amazingly, and turns out NOTHING was wrong with the mass air flow sensor according to the codes and my handy dandy Haynes manual, but their was an issue with the ICV. ICV= Idle-Air Control Valve. It's basically the valve that controls backpressure on the manufold as the engine idles preventing the engine from running to rich. (I noticed when ever the truck would run wierd the exhaust did smell like it was running very rich). I surfed over to Ford Parts Online and found the part I needed "NEW" for about $49.99. I went to Autozone and found an aftermarket one for $39.99. Whats disguisting was the Ford dealership listed that replacement part as costing me $279.99. > I was furious about that, but now I know about this little issue with the 5.4L and 4.6L V8... If they run rough, do you're normal checks first (air filter, check mileage since last fuel filter change, and PCV valve) but remember it could also be the ICV! *BTW the service manager at the Ford dealership said it would take 3.5 hours to replace the ICV valve... TOOK ME 30 minutes! It's easy to replace. If your rough idle isn't corrected by means that you've tried, give this a shot.

Another note... If you are using a K&N oiled Air Filter or another off brand oil air filter... DITCH IT!! I had one on my truck and it gummed up everything. I had to clean the Mass Airflor Sensor with some carb cleaner and a Q-Tip after I learned my lesson with those. They are garbage. It was another reason my ICV began to stick as well.

 

SoonerKA1999,
THANKS SO MUCH!! for all the detailed information. I am going to work on my F 150 this weekend and see if I can sort out the idle issue. I will let you know what I find.
Sincerely,
Don D

 

LxMan1,
CONGRAT'S!!! YOUR THE MAN!!
You nailed it,I probably never would have found it. Turned out it was the PVC elbow that hooked up to the back of the intake manifold, just like you said. Put new one on from dealer and purrs like a kitten. If your ever in San Diego I owe you a steak dinner and a Corona! Not kidding; if you ever come out here ,give me a call 760-518-1194; I torch one mean T-bone or filet mignon. Many thanks again!!!!
Sincerely,
Don D

 

SoonerKA1999,
Turned out my rough idle problem was caused by a burned and cracked PVC elbow that hooked up to the back of the intake manifold.Put new one on from dealer and purrs like a kitten. Thanks again for all your information and I will archive it for my idle issues in the future.
Sincerely,
Don D