'99 Ranger still rough idle

[chucktone]

Have had this truck for a few years now and this past fall it developed a rough idle. Asked an online tech about the problem (had OBDII codes of P0171 and P0174 - Sys too lean bank 1 & 2). Was advised to clean Mass Airflow Sensor (done), replace EGR valve (done), EGR Vac Sel. (done) and if those options didn't work to replace DPFE (done). Engine still has rough idle and same OBDII codes reappeared. What am I missing????

Thanks in advance!
Charlie

 

[Nathan123]

Perhaps an upper or lower intake leak, I believe these rangers are somewhat known for having leaky lower intake gaskets.

 

[PRanger]

I cleaned out my Idle Air Control which sits on top of your Throttle Boddy. Used to idle fairly high now it idles in PARK at about 1.3k when its COLD. Was at 1.7k roughly before i cleaned it. Unscrew it and spray "Throttle Body Cleaner" in it. It says on it not to clean it because of a coating but the Throttle Body Cleaner is OK to use on coated things. Really easy to do take you about 15 min and $5.

 

[Earl43P]

Perhaps an upper or lower intake leak, I believe these rangers are somewhat known for having leaky lower intake gaskets.

Agreed, if it's a 4.0. Read this: http://www.explorerforum.com/forums/showthread.php?t=171819

If it's a 3.0, look for a cracked PCV elbow.


Welcome to The Ranger Station!

 

[chucktone]

Excellent info, thanks again. And thank you, Earl43P, for the link. Indeed mine is a 4.0L. Just finished the job up a bit ago and it is purrin like a kitten.
Replaced both the lower gasket and upper gaskets, EGR tube O-Ring as well as the injector O-Rings. PCV valve too, just for good measure. Read a few times in that forum link where others were having the same MIL codes reappearing after different lengths of time. Personally I think that's probably due to a lack of proper cleaning and prep of the surfaces but I can't say that for sure. Being a retired Ford worker I'm a stickler for details and clean work. Thanks again!!!!! Here's to another 196K!