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I have a 99 2.5 atx. The car eund fine at higher rpms and while driving but when it idles its rough. Rpms go anywhere from arround 1700 to like 100 to the point taht it almost dies. When it almost dies theres like a clunk and then the rpms go back up??

My mechanic at work said it could be the egr valve or a vaccum leak?? How do you find a vaccum leak?? I reset the computer then decided to take it to autozone later to be tested but the CEL wasnt on so they couldnt test it.. On the way home the light came back on.???

Any help would be appreciated
 

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If it is a vacuum leak in the emissions system, you will be able to hear it if you pop the hood and start the car. Listen up near the firewall (behind the upper intake manifold and around the intake itself). A leak is pretty loud up there, you'll hear a hissing sound. Most likely it's not a leak though. It could be a bad egr valve, but more likely a bad iacv (intake air control valve). This is the valve that controls the air going into the manifold at idle. It's the silver cylindrical thing on the back of the upper intake manifold near the firewall. It has a bypass hose from the intake going into it. They go bad all the time, and you can't really clean them. I think fordpartsonline.com has them for around $60 or so. Easy fix and replacement, the bottom bolt sucks, but other than that it's a 10 minute job.
 
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Thank you for your respoinse.

I took the cat to autozone and had them test it. They got codes p171 and p174 lean bank 1 and lean bank 2. I got this code a few months ago and they said change the o2 sensor so we did and a week later the CEL came back on but the car was running fine. so this time they said to replace the fuel filter. I did and at first I still had the problem. But later on that night it seemed like the problem went away. The car ran great all weekend and when I started it this morning it was fine. But on the way to work the CEL cam back on. Then after work when I started it it started idleing rough again. I also notice a slight surge wne I hold steady on the gas ans even when I am off of the gas it will surge slightly and give itself a little gas. So today autozone pulls the same codes and the car gives me codes 9201 and 9318.???

What do these codes mean?
 
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Thanx man I will try the iacv and see what happens. I thought that round silver thing was the egr?? If that is the iacv where is the egr???
 

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I have the same problem!!! Where might the IACV be on an I4?
 

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let me tell you, i just had this problem yesterday, i took it up to the mercury dealer, and a few hours later i found on it was the coil pack had bad, so if you are still not sure got get a diagnostics check.
 
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Thats what Im gonna do. Get a diagnostics check. I reset the computer and everything was fine for 3 days, But today the CEL came on again with a DTC of 9201. I have been told to change atleast 5 different things and they each cost atleast $50 So instead of swapping parts im gonna get a check and find out what one part is messing up.

Thanx for all of the help though guys. This is a great board
 
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