Rough Idle!!!

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Aug 4, 2005 | 01:15 PM

bauerexpy4x4

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Rough Idle!!!

My 1998 Expedition W/5.4l V8 Suddenly Started To Idle Very Roughly. The Initial Trouble Codes Were Iac Valve Value Too High And Running Lean On Banks 1 & 2. I Replaced The Iac Valve And Also The Fuel Filter.
I Have Checked Vacuum Hoses By Spraying With Carb Cleaner While Engine Is Running(no Change In Rpm=no Vacuum Leaks). I Also Checked Pcv Valve And It Is Functioning Normally. I Just Changed The Engine Oil And Cleaned/oiled The Drop-in K&n Filter. My Local Garage Keeps Telling Me To Change This And That, But I Am Already Over $100 Into Replacing Parts With No Results. Any Ideas? (shadetree Mechanic=too Cheap To Trust Garage)---

Aug 4, 2005 | 01:24 PM

2003EXP1

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Mass air flow

Check your Mass air flow it may be going bad check for more codes.
It should be in the air filter box with two clamps.

Aug 4, 2005 | 01:27 PM

Garyl53

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My son's Explorer had the same issues after replalcing same parts as you did. Turned out to be a leak in intake manifold. Much $$ to fix!

Aug 4, 2005 | 01:35 PM

bauerexpy4x4

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I did not have any MAF codes, and I hope my intake manifold isn't leaky! I have heard of them not being torqued properly, but it doesn't seem like that would cause such a sudden problem. It literally started all at once. It also runs fine off of idle and makes a loud hissing sound when the engine is idling(high vacuum time).

Aug 5, 2005 | 07:18 AM

bauerexpy4x4

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I spent $175 for nothing! It turned out to be the end of the PCV hose that you can't see. It attaches underneath the IAC valve, which up underneath the dash on the firewall. I call this area "The Darkside" of the motor because it is the worst place to have any problem on your Expedition/Navigator/F150!!! Thanks

Aug 5, 2005 | 09:48 AM

DIESEL69

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Diesel69

My 97 Expedition just started giving me codes 1131 and 1151 also. no rough idle but after clearing codes they return only on heavy acceleration. i have checked for vacumm leaks, changed fuel filters and pcv. I suspect problem with injector flow or fuel pressure. Any other suggestions?

Aug 5, 2005 | 10:10 AM

bauerexpy4x4

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I don't have the codes in front of me, but they are listed in back of the Hayne's repair manual(possibly chapter 6). It could be MAF sensor or IAT sensor going out. Until you check voltage and resistance specs on the wiring harnesses located at each sensor, it's hard to diagnose. A problem with any of these sensors can cause trouble codes associated with the others. If you have a good digital voltmeter and a repair manual, you should be set.