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Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 23827
Experience:  Certified Subaru Technician, factory trained by Subaru.
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Subaru 2.5xs: I have a 2003 subaru forester 2.5xs It idles

Customer Question

I have a 2003 subaru forester 2.5xs It idles fine when the car isn't moving but when driving it surges and when i put it in neutral at speed it continues to idle up and down like 900 to 2000 rpm but when i stop at a light it idles normally with a/c on or off
Submitted: 1 year ago.
Category: Subaru
Expert:  Mike V. replied 1 year ago.
Hi there,Is the check engine light on?
Customer: replied 1 year ago.
No
Expert:  Mike V. replied 1 year ago.
Ok,It sounds to me like either a fuel pressure issue or possibly an issue with a plugged catalytic converter.Since both of these would cause this type of running issue without setting a check engine light. The fact that it idles ok, but under load has this type off issue leads to these two possible issues.The fuel pressure should be and stay at about 35 psi when you are running at idle and also when you are cruising down the road. To test the converter you can remove the upstream O2 sensor from the exhaust and see if the problem is gone. The car will be loud when you drive it, but if it's the converter, the exhaust back pressure will blow out of the hole and the car should run better.Please let me know what more I can do to help you with this.What happens next:Just Answer will now charge you for the full amount of your question.My goal is to provide you with 5-star service. If you cannot rate me at least 3-5 stars, we will keep working on this.Just Answer does not compensate me for my time and effort; you do with a 3-5 star rating.Follow up questions are included in your question price even after rating.
Customer: replied 1 year ago.
But there is no load when I put the car in neutral and it continues to idle up /down and while in neutral as long as I make a complete stop it returns to normal idle. But won't while coasting in neutral maybe vacuum modulator but I don't know if it has one?
Expert:  Mike V. replied 1 year ago.
Car doesn't have a vacuum modulator on it. The things I gave you to check are the same things I would look at if it were in my shop.One other thought would be the EGR valve. If it's sticking open it might cause this. Normally however you would get some type of egr code. You can unplug the vacuum to the egr and plug it, then test drive the car and see if there is any improvement. If the egr solenoid is pulling vacuum even when it shouldn't be I could see it causing this type of issue, and it would kind of be a hidden vacuum leak. Meaning you might not see it when checking for leaks.
Customer: replied 1 year ago.
I did everything you suggested except I can't find the EGR valve
I don't think the car has one. Problem still exists what else can I do?
Expert:  Mike V. replied 1 year ago.
It is possible it doesn't have the egr, some do and some don't. I believe the manual transmission model has one but the auto doesn't.I think the only other possibility without a scan tool that can read live data would be a replacement front O2 sensor. I have seen them fail without setting the check engine light and cause issues with the fuel mixture. To be 100% honest when I have seen this the car will have hesitation and usually search for idle.If you have a scan tool that can read the fuel trims, both long and short term we could likely tell if its a problem or not.

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