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  #1  
Old 03-15-2005, 10:41 AM
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rough idle after cleaning throttle body, IAC, and EGR

I have a 1997 F150 XLT 4.6 4X4 SC. I got the P0401 code, EGR pressure error, so I took off the EGR, IAC and throttle body and cleaned with throttle body cleaner. The ports on the bottom of the throttle body from the EGR were completely plugged with carbon so I cleaned them out so they are now open like they should be. When I was cleaning the IAC, the rod seemed to be sticking somewhat so I used a screwdriver to work it back and forth. I could move it to one side and it would stay put, then I could move it to the other side and it would stay put there. The spring wouldn't retract it, but I don't know if that is how it's supposed to be or not. I put everything back together and it was fine at first, but now 4 days later it is starting to idle rough when it is warmed up and sitting at a stop light, stop sign, etc. Once I take off it is fine with the exception of two or three times it has stuttered under steady speed, like it was starving for gas. Just kind of shuddering. Once I push the pedal down harder, it catches back up and is fine. Does this sound like the EGR is stuck, or is the IAC rod stuck and not moving freely enough, or something else? I hate to start replacing parts not knowing which of them is most likely the culprit. Sorry for the long post, just thought all of this information could help the diagnosis. Thanks ahead of time for any ideas.
Kurt
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  #2  
Old 03-15-2005, 10:54 AM
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egr only come on when ur cruising. iac is likely sticking get a new one they are cheap
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Old 03-15-2005, 11:48 AM
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I agree, you probably need to replace the IAC. It shouldnt stick like you were describing.
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Old 03-15-2005, 12:14 PM
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In addition to the IAC, it's also common for spark plug wires to come loose when working on the EGR system. You may just want to try reseating the plug cables on the right hand side of the engine.

A loose plug cable will cause a rough idle and vibration when at a stop light. You won't notice it when driving at higher speeds.
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Old 03-15-2005, 12:16 PM
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how could u hit a spark plug when messin with the EGR?
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Old 03-15-2005, 02:46 PM
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Also...

I've been having the rough idle condition for the past three months and last nightI noticed that when going down hill I smell the gas. Any ideas guys?????????????
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Old 03-15-2005, 03:37 PM
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Quote:
Originally posted by Faster150
how could u hit a spark plug when messin with the EGR?
On a 97 4.6L, the plug wires are right underneath you when removing the EGR valve and DPFE sensor. It's fairly common for home mechanics to knock loose a plug wire when working in this area. I've seen it a dozen times. They may, or may not, get a Check Engine light for the missing cylinder. But, they will notice some vibration and rough idling when stopped at stop lights and such.
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Old 03-18-2005, 12:57 PM
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UPDATE:
Okay, it finally threw a check engine light so I had Autozone pull the code and it is the same P0401 EGR pressure code. I have already cleaned the ports so I know that isn't the problem. It is running really bad at idle once warm. Do I need to just replace the EGR, or is it something else that is causing this?
Thanks,
Kurt

Edit: Could it be the DPFE/EGR Position sensor? I have seen people say in previous posts that if you apply vacuum to the EGR and the engine stumbles/dies, then the EGR valve itself is okay. I know this is a newbie question, but how exactly do you apply vacuum to the valve? Through which port, the one on the top?

Last edited by clvlndta3; 03-18-2005 at 01:07 PM.
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Old 03-18-2005, 11:39 PM
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Take the vacuum line off the egr. Find another vacuum line thats getting a good vacuum. With the engine running, attach the newly found line to the EGR. The engine will die right away ( if the EGR is good, or so I am told by other memebrs here ).
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