First off I want to say "Thankyou" to all who have given me support in this endeavor! In spite of everyones best effort I am unable to resolve my 4.0L idle problems! Briefly I get ce light? Purchase OBD ll code reader and get IAT sensor code? I replace with new $40. Reset PCM and new ce light, 0171 and 0174; everybody get's these! After reading Rockledges post I decide to let Dealership diagnose before I go ahead? They come up with same codes and recommend new intake manifold gaskets, fuel rail gaskets, injector O rings top and bottom and EGR O ring. I purchase gaskets from dealer $126. and install myself saving nearly $600 in labour? Ce light goes away but still idles poorly? I have checked vacuum hoses and reset PCM several times to no avail? FTE suggest problem may be other items? Plugs, Wires, O2 sensors? Parts store recommend Plugs and wires before spending on O2 sensors and I agree $130. Problem still exists? More FTE input and I clean IAC sensor! Now the truck barely runs? Cleaning IAC seems to have made things worse so back to the dealer and buy a new one $190 plus $10 for a gasket? Reset PCM several times still no luck? Damn I am frustrated!!!!! Pride doesn't want me to crawl into the dealer and ask them to fix this? I am really pissed! Thanks for your ear's.

 

Did you ever replace the plugs, wires, and O2 Sensor? Maintenance items like those, which have a service life, are things worth replacing in a situation like this, unless they are very new. Plug wires can fool you in appearance, plugs widen their gap with erosion, and O2 sensors get sluggish and eventually fail. Have you checked the vacum line on the FPR for fuel? Do every simple, DIY diagnostic you can possibly do, and having a scanner you can do quite a bit, if you don't find anything obvious, replace service items that are near their limit and clean every sensor that requires it. Resetting your PCM will do nothing if you have a real problem, the computor will just relearn the faulty imput all over again, the fact that this problem persists is a good thing, it's the intermittent ones that are hard to find. If you keep at it, you'll find your problem. And don't replace a non-service item unless there's no other way to rule it out, that's how DIYers end up spending more money doing it themselves!

 

Yes I have replaced the plugs and wires! I changed everything I spoke of in my rant! The only items not changed are the two O2 sensors which are located (one upstream and one downstream of the cat. converter in the exhaust system! I find it difficult to believe they could control the idle to the point that the truck is now running so poorly? The most dramatic change occurred when I cleaned the IAC valve and after doing so the idle got worse and then I purchased from Ford a new IAC valve with no change to idle performance!

 

DPFE?? didn't see it mentioned in you list. also, the o2 sensor could cause it. probably not likely, but they could. also, if you did fix the original problem in the time it was off it may have been running rich for instance and taken a toll on your o2 sensor(s).

 

Does it clear up once you give it some throttle?

Also by cleaning your new IAC, you may have actually damaged it.

Try unplugging the IAC, and hold the throttle open just enough so it is at normal idling speed (remember you'll need to hold down the pedal a bit while starting as well, and if you let off the pedal, the engine will stall), If it still idles rough, then you can rule out the IAC.

 

Hey jmgrif,

With total respect: Dude! YOU ARE DEFINATELY NOT ALONE! If the PCM isn't getting the proper signal the O2's are other items to consider and acquiring a VOM or DVOM is a prerequsite to diagnosticians...like us!
And when you get a moment check out my posts & look at all the crapola & possible resolutions offered me by FTE'rs.
And to boot I will trade you frustration factors cause I'm there right along side of you...MEGGA PO'D!!!

 

Do you think the O2 sensors could cause the engine to idle so poorly? As this project has gone along the idle has progressively gotten worse! I don't have a multi meter either or a fuel pressure gauge so I am limited by those two items missing from my tool chest?

 

The O2 controls the fuel trim mixture, if it/they sense a lean condition when it doesn't exist, they will signal the PCM to increase the pulse width and the mixture will become too rich, and the opposite can happen as well to cause a lean condition. Did you pull off the vacum line at the FPR? Your symptoms sound exactly like a '92 dually I used to drive for work that had an FPR die. Just a suggestion.

BTW, the downstream O2 isn't likely the problem, the first O2 is the mix sensor, the downstream O2 compares it's reading with the first to determine if the Catalytic converter is working.

 

at this point, the way i see it youve put in enough time and money what would it hurt to try the o2 get one from autozone and change it in the parking lot if it doesn't fix it, take it back, if it does then you're all set. good luck hope it works

 

OK here is today's story! First I have to back up a little? Yesterday afternoon I replaced not 1, not 2, but all 3 O2 sensors! That did not improve things one little bit! Didn't sleep well last night and drove into Ford dealer this morning to let them have a go? They couldn't do very much due to the large vacuum leak at the tube from the EGR that enters into the Intake manifold and has an O ring on it that I replaced in the beginning of my project? The technician tells me he often puts 2 O rings on and lubes them up with vaseline? He also pulled one plug and told me the gap was to big, so I guess I wasn't careful enough gaping them but I was pretty sure I was at least in the ball park of 56thou. Anyway I will pull them all a recheck? Now when I get home I pulled the intake to look for the new O ring I had carefully put onto the EGR tube and had made sure it wasn't pinched or anything and it was there but one side of it looked like it had been pulled a little probably causing the vacuum leak spoken of by the Ford tech. I found the old O ring I had removed in order to replace with the new one and it was not damaged at all so I put in on the tube and the new one on top of the and liberally spread vaseline all over them and replaced the intake and went for a drive! Things have improved... a little... of course I had the battery disconnected for the time it took me to re and re the intake so the PCM should have had time to unlearn it's bad behavior but there is still a little surging when idling but not nearly as bad as it had been? I will let things cool down and check the plugs later tonight and update after that!

 

hi jmgrif,

I know what you've been through and just to show you that are there others w/ megga problems click on the link below and scroll down to my latest post:
https://www.ford-trucks.com/forums/7...tuation-2.html

You'll be shaking your head as well as I.

Joseph / crazypaw

 

I would have suggested the dpfe and iac sensors. I wouldnt clean an iac, i would throw it away and get another. I cleaned mine on my ranger and it worked (for about a week) than it was back to its old antics.

also, 56 thousands? i thought correct was 44-46?!

Matt

 

I had all of the same problems on my 99 B4000, turned out to be the #5 exhaust valve. Up to my elbows as I speak! Good Luck!

 

I haven't done a compression test yet, but a friend did suggest valves as a possibility? Did you get ce light after doing all the above but before you discovered the valve problem?

 

The answer is Yes. Here is a link to my plight. https://www.ford-trucks.com/forums/6...ough-idle.html