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PostPosted: Sun Mar 09, 2008 12:47 pm 
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Joined: Sat Mar 08, 2008 6:59 pm
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Hi-I just bought my first Subaru-a 1990 Legacy wagon with 121k miles. Car runs well and has been well cared for. I have one problem: The idle goes up and down-fluctuates. We replaced the idle control unit at a substantial cost but the idle problem still exists. Any thoughts on what I should do or look at next?


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PostPosted: Mon Mar 10, 2008 6:26 am 
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Joined: Mon Jul 30, 2007 9:11 am
Posts: 48
Location: Buffalo, NY
Hi John and Image to the board!

Check for vacuum leaks. On a vehicle of that age some of the vacuum and other hoses might be cracking/brittle/etc. The easiest way to check for vacuum leaks is with an emissions smoke machine. This injects a fine smoke into the system under low pressure via any conveninently available vacuum line, and anywhere you see smoke seeping out indicates a leak. These machines are pretty expensive so a shop would probably need to do this test for you.

If you already replaced the IACV - idle air control valve, and the new valve is good, then that might not be a problem. I like to spray some throttle body cleaner into this valve's intake with engine idling to clean it out good. When you spray the cleaner, the engine will stumble a bit, and the IACV will be excercising more open and then closed as a result (good for cleaning it out).

Also if the IACV was replaced, but a new gasket was not used, there may be a leak here too.

Here's a pic from my '94, your '90 might be alittle different though.
Image

john sellers wrote:
Hi-I just bought my first Subaru-a 1990 Legacy wagon with 121k miles. Car runs well and has been well cared for. I have one problem: The idle goes up and down-fluctuates. We replaced the idle control unit at a substantial cost but the idle problem still exists. Any thoughts on what I should do or look at next?


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PostPosted: Mon Mar 10, 2008 8:21 pm 
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Joined: Sat Mar 08, 2008 6:59 pm
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Thanks so much for the response. We did find a leak and repaired but now it's not passing CA smog because it's running too rich. Replaced plugs and ox sensor but still too rich.How much is a mass air flow sensor on these?


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PostPosted: Tue Mar 11, 2008 9:45 am 
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Joined: Mon Jul 30, 2007 9:11 am
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Location: Buffalo, NY
Hi. If you mean a new MAF from Subaru, those are about $400. A used one from a salvage yard hopefully a lot less.

What brand/type o2 sensor did you use? Do you have any exhaust leaks? How do you know it is running too rich? Soobs like NGK spark plugs. If you didn't unhook the battery during the work, you might try unhooking it for about 30 minutes to let the ECU forget all its old settings, and relearn the fuel trims, etc.

Tips I have heard for passing the test (maybe you already did these): make sure vehicle is at operating temp before the test (i.e. at least a nice 10-15 mile drive), do not shut vehicle off at testing station - leave running until your turn, put a few bottles of isopropyl drygas in the tank.


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