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Idle Trouble Rev n Stall? 91 legacy LS


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91 Legacy LS wagon, Auto, 2.2L. Lately, after a few minutes driving, the check engine light comes on, and when idling, the rpms rev for a few minutes, then it backs down to nearly a stall. sometimes it does stall. If I'm trying to get across town and keep the rpms up and make the stop lights, i can keep it going without stalling. fuel pump? timing belt? suggestions?

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It's an IAC valve problem. I had it on my 91 Legacy. And IAC valves are not fun... :(

 

I tried cleaning mine with carb cleaner and only gunked it up instead; since it was my only car then, I bit the bullet and bought a shiny-new IAC valve from the dealer for a mere $362 :eek:, which is a royal PITA to install too. I probably would have tried cleaning it with brake cleaner, which I suggest you try. That will evaporate and not leave any residue. Take the big hose off of it that runs from the intake hose and spray some cleaner in there, and wait for it to evaporate before starting the engine... Just be careful though, it's a delicate instrument.

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Thanks! I'll try the brake cleaner trick. I replaced an IAC valve on a domestic car and still can't believe i got it done right, but it works. Yours sounds like quite a bit more money.

 

I found the ECU trouble codes using directions on this site:

Four problems going on according to morse code from engine light -

O2 sensor, starter switch, AF learning control, and Air flow sensor.

 

Called auto parts for prices of O2 sensor - $50

Air Flow sensor is $220 with $30 core refund.

 

My question is: if I get these used at local junk yard, is it worth risking used sensors from a junked car with only 60K mi. AND / OR since the black wire trouble code test also tests prior problems, how do i know these problems haven't already been fixed but the last mechanic didn't clear the codes?

thanks.

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Thanks Josh,

 

I reset the ECU, ran it in D-mode. That was a good trick b/c now the only code coming up is 41 - A/F Learning Control. Happy to only replace one thing instead of four, but what the heck is it? Asked at the auto parts store, they didn't help.

Any help?

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a/f learning control is the ECU. That's a rather weird code to have show up.

 

After you cleared the other codes and ran d-check, did the car stall and run weird? How has it been running since you cleared the other codes? Did any other codes come back after driving it for a little bit?

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a/f learning control is the ECU. That's a rather weird code to have show up.

 

After you cleared the other codes and ran d-check, did the car stall and run weird? How has it been running since you cleared the other codes? Did any other codes come back after driving it for a little bit?

I haven't driven it much since I don't want to damage something any worse. After I cleared the codes, I started it in d-check, it still revs some and rpms slow down but it doesn't stall lately. When I did test drive it, I give it gas and there is a delay in the response from the engine, like it isn't getting the air / gas that it needs for a moment.

 

My plan is to check the PVC valve 'cause it's easy, then spray some brake cleaner on the IAC. Will let you know what happens. Any other guesses I'd love to hear it.

 

btw - I just bought the Chilton's, this is getting serious!

 

Brian

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91 Legacy LS wagon, Auto, 2.2L. Lately, after a few minutes driving, the check engine light comes on, and when idling, the rpms rev for a few minutes, then it backs down to nearly a stall. sometimes it does stall. If I'm trying to get across town and keep the rpms up and make the stop lights, i can keep it going without stalling. fuel pump? timing belt? suggestions?

My daughters 2.2 Legacy had idle problems hot and cold but there were no alarms. I checked the Haynes manual and did all the recomended things like plugs, air filter, clean throttle body, check for vacuum leaks. I also tried to remove the Iac valve but gave up because of the difficulty. However the Iac valve did not seem likely because it is supposed to to be closed when hot and I simulated that by pinching the hose. All that did was stall the car.

So in the end I gave up and sent it to the dealer who fixed it quick. Vacuum leak on the inlet manifols gaskets. He replaced two of them.

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My daughters 2.2 Legacy had idle problems hot and cold but there were no alarms. I checked the Haynes manual and did all the recomended things like plugs, air filter, clean throttle body, check for vacuum leaks. I also tried to remove the Iac valve but gave up because of the difficulty. However the Iac valve did not seem likely because it is supposed to to be closed when hot and I simulated that by pinching the hose. All that did was stall the car.

So in the end I gave up and sent it to the dealer who fixed it quick. Vacuum leak on the inlet manifols gaskets. He replaced two of them.

The saga continues...

Replaced the PVC valve today. That was cheap and easy and seemed to help some. I noticed the hoses have a good buildup of gunk on the insides. I tried cleaning one out but assume all of them are booger-lined. I disconnected the hose going into the IAC valve and sprayed a good 4-5 long shots of brake cleaner in there. Turned it over a few hours later and ran ECU in d-check mode. Code 41 is still coming up on test drive, but the problem seems to have gone away mostly for now. It still revs a little in short intervals. When I turn on A/C max or normal it jumps up some. I'm going to try and drive it to work tomorrow and see if it acts different cooler in the morning. Maybe I can just put a smiley sticker over the engine light? icon10.gif

 

Once this is over, next up is window tinting, new visor (broken), alignment, and playing with non-responsive front air struts.

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if you're still getting code 41, I'd say it's a pretty sure fire bet the ECU is having some issues. You can clean whatever you want, but you're still going to have issues.
Isn't owning a subaru a sure-fire bet the owner is in store for some issues? icon7.gif

Yesterday, on my commute to work, engine was cold and light was blinking away in D-mode, as usual. When I gas it, the rpms go down until I get up to 15-20 mph. Then, during lunch, I looked at the blinking check eng light and it was flashing in 1/2 sec intervals!!!! All clear mode! (I routinely clear the ECU lately - hoping this would happen.)

 

Instantly, I disconnected the black and green wires and the light WENT OFF!!

 

of course, it came back on a hour later, but I see this as a start? Maybe it just took awhile for the brake cleaner and all it's gunk to get outta the way of the IAC? 'cept for the morning drive, seems to run fine, just an intermittent eng lit.

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if you're still getting code 41, I'd say it's a pretty sure fire bet the ECU is having some issues. You can clean whatever you want, but you're still going to have issues.

 

Replaced what I thought was the IAC, but it wasn't that hard to replace so I doubt I got the right part. Parts store called it a bypass air console or something. Anyway, while driving around town, I stopped to put some air in rear tires, they were very low with a slow leak, and as soon as I did that, guess what?

 

The engine light went into all clear mode! I don't know if this is even possible, but could having low tires tell the ECU that the car is having to use too much power to move so it thinks there's a problem with how much air to mix with the fuel?

 

It sounds like a long shot to me but the light hasn't come on since in two days of driving.

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Replaced what I thought was the IAC, but it wasn't that hard to replace so I doubt I got the right part. Parts store called it a bypass air console or something.

Where was this part located? Can you find where it is on any of these pictures? http://www.main.experiencetherave.com:8080/subaru/images/injectors

 

Anyway, while driving around town, I stopped to put some air in rear tires, they were very low with a slow leak, and as soon as I did that, guess what?

 

The engine light went into all clear mode! I don't know if this is even possible, but could having low tires tell the ECU that the car is having to use too much power to move so it thinks there's a problem with how much air to mix with the fuel?

 

It sounds like a long shot to me but the light hasn't come on since in two days of driving.

There is absolutely no electrical connection the ECU has with tire pressure. I'd say what you experienced is pure coincidence, and/or the ECU finally had enough drive cylces of everything being ok for it not to freak out.

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Where was this part located? Can you find where it is on any of these pictures? http://www.main.experiencetherave.com:8080/subaru/images/injectors

 

The part is listed on your link as the IAC valve. It has the light brown plastic top with electrical connection. There were some hoses in the way to disconnect and reconnect but four bolts wasn't as hard as other people have reported.

 

I sprayed the new-used IAC with brake cleaner before installing it. The car seems to be running worse. It usually coughs a little starting cold then runs like a top most of the time. Then, after a few miles or even a half hour, it will decide to vomit and I lose almost all rpms, the gas pedal does nothing and when I feather it, all I can get is clouds of black smoke out of the tailpipe. After it sits for a half hour or more, it usually is fine and runs like a top again. It's confusing since it's not an all-the-time thing. Engine light only comes on when it's coughing, then goes off. Any ideas?

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These are happy days. I read the article on high octane gas in another thread. It reminded me that I filled up recently with 91 octane thinking it might help clean out the engine. That's when it started running worse. Today I filled it up with good ol' 87 and she purrs like a kitten, for today anyway.

 

No engine light, power when I want it, and no stalling in the middle of an 8 lane intersection.

 

 

 

Brianicon14.gif

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Well, happy days are over. Problem is progressing. It runs great for about 30 minutes then while driving down the road with the pedal held consistently, the engine suddenly drops rpm. It is a shocking thing to have happen, and I automatically take foot off gas. When I do, the rpms lower, then rise, then lower, then rise. It's like someone is feathering the gas but it's not me.

 

My only remedy now is turn on hazard lights, floor it until the engine catches and it surges ahead 15 feet, coast until it catches again, etc. Then finally when I can pull into a parking lot, turn it off and let it rest with ignition off for 5-10 minutes. Then all is well again. I've read some similar posts and wonder if I should try changing the MAF sensor? Anything else?

 

Thanks - Brian

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Ran the diagnostic test this morning. Code 41 came up again and code 23 returned after a month vacation. 41 is nothing new - unsolved problem, but 23 is Air Flow Sensor - same as MAF I'm guessing? I plan on looking for a cheap used one at the local yards today unless anyone else has a better idea what could be causing the erratic idleing.

 

Brian

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The weakest link on modern cars (especially with accumlated mileage) is easily the integrity of the wiring harness and connectors. Just have a look at the diagnostic section in the rear of the Subaru manual. 9 out of 10 proceedures for tracing down possible causes for the indicated codes end up being for checking continuity between two points. Before you get into a parts-swapping fit, get a multi-meter and a Sube manual and do some harness checking.

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The weakest link on modern cars (especially with accumlated mileage) is easily the integrity of the wiring harness and connectors. Just have a look at the diagnostic section in the rear of the Subaru manual. 9 out of 10 proceedures for tracing down possible causes for the indicated codes end up being for checking continuity between two points. Before you get into a parts-swapping fit, get a multi-meter and a Sube manual and do some harness checking.

Thanks! I'll check that out and keep updating.

 

(today, took the wife to a very fancy brunch for a rare treat. On the way home, engine got sick and we sputtered black smoke for most of 12 miles in 100-degree heat. kinda took the edge off the romantic morning.)

 

brian

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Took the car to a good mechanic. They ran a full diagnostic test on everything air / fuel related. Everything checked out except the MAF sensor. It's good piece of mind to have the second opinion when I was already leaning there.

 

I'm now looking for the cheapest / best option to replace. Auto parts stores sell them reman for $210. I think I saw one at jy for 30 or less - any harm in going the cheaper route ? I can always just replace it if it goes out as well..

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