legacycentral bbs

Ok, All you really smart people!

My 1991 Manual has developed a really weird idle.

It is cold here in Canada now - way below freezing last night.

Car has 160K miles

Car started very well this morning, yesterday it cranked, and cranked and cranked and finally hit.

Most of the time the car runs very well off idle - excellent and smooth.

BUT!

It seems to have two modes:

1, Really low idle, 500 rpm or so - rough idle, bounces up and down a little, sometimes when I take off the gas, it almost stalls, 'till it jumps up to 500 RPM

2, Really fast idle - 1800 RPM, constant, length of time driving does not matter, it WILL NOT go down. Turn off and on will not help.

The car gets a good run - 60 miles of commute style driving, with 3/4 above 60MPH every day.

I also get random Check Engine Lights, which go off by themself usually in 10/30 seconds.

My mechanic is a Subaru Delaer, and has been doing it for years.

I have had it in several times to fix this, I usually get a cleaning of some sort, and it is ok for 1 day or so.

Last time I was in I mentioned how many times I have tried to fix it, and he said it is because I have the "old" intake sensor thingy. He could replace it with the newer one, and the troubles would go away.

Anyone have any ideas? - it is really beginning to bug me.

Dirty IAC valve.

The procedure has been posted a couple times on other sites, but in short you have carbon dust build up that is making the idle controller stick. Easiest way to clean:

Remove pcv valve
Remove top (electronic portion) of IAC
Remove hose for the IAC at the intake side
Fill hose with plenty of carb cleaner, while turning the valve
Fill the tube again and this time blow while turning, air and cleaner will escape through the PCV valve hole

Repeat as needed. You should feel ZERO drag when turning the valve. Reassemble and try it.

Ciper,

Thanks a bunch, and I will look at it this weekend.

One question, Where is, what is the IAC?

Real n00b

Thanks!

Ok,

A simple search, and I have it.

Thanks!

I've cleaned my IAC valve.....it's definitely not a cure all.....I've got some of the issues your car is exhibiting.

When your mechanic said new intake sensor.....was he referring to the MAF sensor? or something else?

He spoke of replacing everything on the intake.

So, I am sure he means both.

They deal with lots of older Subaru's and I would assume that since they have done it before - It should work.

Tough part is it is almost Xmas - tough time for me financially - really slow at work.

Luckily, the car was behaving itself this morning, after the loooonnng cranking and finally starting, the idle was perfect today.

It is getting too much fuel on cold crank - always blows out black smoke..

Would you mind asking him exactly what part he said to replace.

Thanks

Will do - I will be in there later this week.

He has several parts cars - and at this point - I think I have paid enough to own two of them.....

I will see what he says

*sometimes, i get a funny idle. it will jump around at 350-500 rpm and you have to hit the throttle to keep it going. although, i don't experience this everyday. i just replaced my pcv valve and i tightened my Idle screw adjustment on the throttle body. it helped a little.

Don't mess with that idle screw. It will cause you problems.

The TB is meant to flow a certain amount and is bench tested at the factory.

The ECU is just going to adjust the IAC valve's duty cycle to compensate from you turning the screw.

oh, i actually already moved it back to stock position. where is the IAC in the engine bay?

On the inside fender I believe, under the plastic cover.

totech, not sure if you were answerin about the IAC valve.

But it is right below the PCV valve. I thought I had some pics.....but they don't seem to be around.

There are two coolant lines running into it. You should be able to find it....it's not too hard.

Yep, the IAC valve is just below the PCV valve. The top of it is a little plastic rectangle-like thing mounted in place with two screws.

I actually haven't really found it documented anywhere, but the IAC valve is adjustable. You can adjust it in place if you remove the plastic coil cover and the little metal bracket that the cover attaches to. To adjust it you unscrew the two screws and then the top part of the valve can rotate relative to the rest of it.

That said, I don't recommend messing with it unless it's been messed with in the past. It's probably like the throttle stop screw, not meant to be adjusted after leaving the factory. I tried, though, since my car has a weird idle and I thought it might help. It didn't.

If you still have trouble finding it, let me know and I'll try to get you some pictures.

I am having a funky idle, too, so much so that a strain like steering on full lock will make it almost stall. I will check my IAC valve soon (thanks for the tip, guys! ), and I can also tell you don't play with the TB stopscrew, b/c it is giving the engine gas even when you're starting it, which is not good...

BTW, just in case my IAC valve is due for replacement, anyone know the price of those things? And somebody mentioned MAF sensors. Aren't MAF sensors about $300?!

OK, lots of stuff going on in this post, good to hear everyone is on in this. First, totech, sounds like your Subie Mechanic is taking you for a ride, if he hasn't fixed it yet, he is just soaking you for a few more bucks waiting untill it is broke down on the side of the road or just woun't start at all, and this replacement of the whole intake, which can include the Mass Air Flow Sensor (big bucks for new part) is just BS, if he needs to replace the whole thing, it means that he doesn't really know what is causing the rough idle and is hoping that replacing all the items will actually catch the problem.
Here is what I suggest, I live in the Upper Peninsula of Michigan and we get the snow and the cold like you in Canada and I work on Subies for my old man, mostly Legacy's and Loyals, and have had rough idle problems before. Give this a try, reset your ECU (many ways to do this check the archives here or on the Yahoo Groups) easy way is when your car engine is cold, unhook the negative wire from the battery terminal for at least 30 min. then reattatch the wire to the battery and start your car but don't touch the gas pedal at all and let the car idle untill warm, then take for a ride and go trough all your gears under normal driving condition.
This is my Subie cold weather theory, all the Legacy's I have driven in the summer, run fine, top notch, could weather hits, problems pop up, I think that the quick (1 month) temp change/humidity change to could winter weather can't be compensated by the ECU that is used to running in warmer weather. Reset it to cold weather and it should smooth it out. Also, you mentioned your Check Engine light comming on for a brief moment when cold, try checking your codes when the light is on (again, check the archives on how to do this) and it might point to the problem if it is caused by a sensor or valve. Hope this helps and good luck, john k

Even a very small vacuum leak can cause major idle problems. Check all your intake (vacuum) lines after the MAF.

Thanks guys, too cold right now to check anything, and me with a cold....

Perhaps later this week!

Sometimes the car runs great! 20% crappy.

I love the car otherwise, noisy tranny, clunks, creaks and all.

MAF sensors are 300+ bucks.....I know.....I've bought one.....

IAC valve is not cheap either......try to get one used.

As for the throttle stop screw and it telling the ecu to give gas.....that's not a real issue because you can adjust the TPS to have the idle switch function how it's supposed to

BTW, anyone planning on doing the IAC valve cleaning described here better have at least good knowledge of that specific component. Legacy777 recommends leaving it alone, and now I do as well. You can really screw up by trying to "clean" things...

Update:

I have now caused my IAC to seize. The solenoid can no longer open the valve. So my car is simply driveable b/c I cheated and played with the stopscrew to makeshift a stable idle. Maybe it's because I used crappy carb cleaner, I don't know, but after I put a new valve on, I'm not playing with it again...

I bought a new IAC valve today. Nobody makes a nice, cheap aftermarket valve that you can get from Autozone or anything like that, and there aren't BC-BF Legacies strewn all over junkyards, at least not in FL. So I had no choice but to go to the dealer. $363.95 later, I can officially say that it would be cheaper to check every other alternative solution to a weird idle problem. You can laugh at me if you want, but at least learn from my mistake. I'm just waiting to replace the valve and find my idle to still be erratic thanks to a leaking vacuum hose...

Okay, final post on IAC valve. I put my new one on today, can't say I enjoyed doing it, b/c coolant hoses are completely out of reach. The gasket doesn't come with the assembly, either. At least it idles a whole lot better...

Someone also told me I should have used brake cleaner instead of TB/carb cleaner coz brake cleaner will evaporate; TB/carb cleaner leaves a residue...

All I know is I'm not messing with it ever again!

I know this is a old post and all, but since it's referenced from a newer one.. I'd thought I would chime in.

If you're going to clean the IAC, use CRC Fuel Injection Air-Intake Cleaner. It evaporates, and will not leave a residue -- so you won't have to worry about seizing anything.

Make sure that's for fuel injected engines. I've been doing this for years on 82-92 Camaro/Firebird's, it seems Subaru and GM both share the same IAC issues. This stuff cleans it right up as good as new, and it's about $2.99 a can. Be liberal, make sure that sucker is clean.

I've used some tb cleaner stuff and it left a residue.......haven't used the crc stuff you mentioned......brake cleaner works good