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91 legacy rough idle when cold


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8 replies to this topic

#1 wildseamus

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Posted 23 October 2009 - 06:06 PM

Have a 91 2.2L legacy L Wagon that has a rough idle when cold. The RPMs will surge from about 300 to 1800 erratically until I warm up the car by holding the accelerator down and keeping it a 2000 for a minute or so. Problem only happens when it's cold and car will run and idle normally after warming up or starting when the temps are about 40 or so. It will die if I do not keep the RPMs up when it's cold. I've look all over for a EGR valve, either is does not have one or I just can't find it. All vacuum hoses look good as well as air filter and fuel filter is only a few months old, pcv valve also checks outs.

Help,

Ryan

#2 ericem

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Posted 23 October 2009 - 06:41 PM

There is no EGR on your car. You probably need a new ECU coolant temp sensor or your IAC valve needs to be cleaned.

#3 wildseamus

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Posted 23 October 2009 - 09:33 PM

Thanks I'll look into both of those tomorrow and post what I find out.

Ryan

#4 zyewdall

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Posted 24 October 2009 - 09:43 AM

Exactly the same symptoms as mine ('90 legacy). I tried to clean the IAC valve last week, but a friend has been driving it since then, so I don't know if that helped it or not. He's giving it back today, so I'll check.

Z

#5 hustle

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Posted 25 October 2009 - 08:01 PM

I had the same problem with my 91 legacy. I cleaned the iacv like suggested now the car idles @ 2.5 rpm even when warmed up. I'm so tired of messing with this. Any suggestions?

#6 Log1call

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Posted 26 October 2009 - 01:40 AM

Clean it some more?

If it's got worse it will be because you've disturbed some dirt and it's making the valve stick.

#7 wildseamus

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Posted 30 October 2009 - 10:34 PM

Cleaned the crap out of IAC and throttle body and replaced the coolant temp sensor as it was a bit questionable when I did a resistance (ohms) test. Replaced coolant hoses to IAC as they were a bit swollen....and I actually cut the old one off to facilitate removal of IAC. Now she runs smooth, no rough idle. Only driven her about 20 miles since repairs but so far so good. Started easy on a 15 degree morning.

Started cleaning IAC with rubbing alcohol and Q-tips....finished it off by soaking it in gas (removed electrical sensor) for a 1/2 hour and rinsed with alcohol to clean off the gas. Dried it off with a blow-dryer......came out really clean. Was a bugger getting the new coolant hoses reattached, other than that it wasn't too bad of a job.

Cleaned throttle body with carb cleaner and Q-tips while the IAC was removed.

I believe the major problem was a dirty IAC. I tested the resistance between my new and old temp sensor and pretty much had the same results in the freezer and in boiling water.

Edited by wildseamus, 30 October 2009 - 10:44 PM.


#8 hustle

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Posted 30 October 2009 - 11:13 PM

.and I actually cut the old one off to facilitate removal of IAC. N.


I really thought about cutting this off too. It took me about an hour of fiddling with it until I finally got it off. I used gas to clean it up too, but wasn't thorough about getting it dried out before reinstalling maybe that's why it's idling at 3000 rpm now. I'm hoping it's just the gas burn off and not a stuck valve. I haven't had a chance to take it for a good drive yet to see if that were the case. I really don't want to have to take this off again...

#9 Fairtax4me

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Posted 31 October 2009 - 11:44 AM

The IAC motor can be adjusted.

Here's a little explanation of how it works from a previous thread...

The idle valve works on a modulated pulse width, that is to say, it is getting turned on and off hundreds of times a second and the ratio of off time to on time is being altered to make the valve wider open or more closed. It doesn't actualy get turned on, or off in the traditional understanding of the word as it would normaly be applied to a solenoid. Whatever sound you heard wouldn't have been the solenoid opening or closing. That's the first problem with trying to use the valve "opening" as your clue to the throttle position contacts opening.
The pulse width is happening all the time, even when the revs are up and you are driving.


The thread is HERE and has some good info in it.

Basically the servo motor has to be set near the center of the allowable travel. It can be fine tuned better than that but you need a laptop with diagnostic equipment or a good scan tool that can read the duty cycle of the valve. I think if you get it close enough you can at least get the idle speed to come back down to a reasonable level.




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