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2000 Legacy L, 5MT ~215k

 

I recently changed the manual trans and took it for it's first test-drive yesterday.  I've got an engine check light.  I'm trying to locate a code reader to find out the code, but in the meantime, lets have some fun. 

 

It ran fine before I took it apart.  After reassembly, it starts fine, runs fine through warm-up.  Once it's warm, the idle is rough, sometimes stalls, usually doesn't, but it only occasionally idles smooth. 

 

I'm thinking that it has to be something I overlooked, screwed up, or otherwise messed up during the trans install since it ran fine before I took it apart.

 

Mass Airflow?  Other ideas?  Give me things to poke over the weekend and I will!

 

Thanks!!

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Vacuum leak is my first guess. check all those hoses to make sure they are on and not cracked.....second has to do with how my 09 impreza reacts to having the computer reset. It seems to need some run time before it gets all its settings in check.

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I switched motors on my 02 legacy L about three weeks ago and it seams like we are having similar problems with poor idle, i have to turn my car off at long redlights sometimes it may or may not have any relation but Im running a diagnostic with my mecanic later this afternoon i will let you know

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Hoses on the intake tube loose. Intake tube clamps loose. Airbox not assembled properly.

 

The 99 and up also tend to have some issues with re-learning idle settings after the battey has been disconnected. Check over all of the wiring and hoses you had unhooked during the work and make sure that's all connected properly first. If all of that checks out, disconnect the battery for about 15 minutes.

Reconnect battey and start the engine, let it idle on its own. DO NOT TOUCH THE GAS PEDAL to keep idle speed up. If the engine stalls, turn the key off, restart it, and just let it idle so the computer can figure itself out.

Allow it to idle until the cooling fans cycle on then back off. If its a cool day this might take a while.

Once the cooling fans turn off, turn the engine off and let it cool for about an hour.

After an hour, restart the engine, let it idle for about 10 minutes, again no gas pedal. If it stalls just restart it. After 10 minutes take it for a drive, about 15-20 minutes in a residential area. Park it, turn the engine off, wait a minute or so, restart and take it for a drive on the highway where you can sustain at least 45 mph speed for 10 minutes or so, then drive it home park it and let it cool off. If you follow that correctly the ECU should relearn proper fuel trims for idle and cruise and you shouldn't have any trouble after that.

 

If you still have the problem after that, something was overlooked like a loose vacuum hose or you have a coincidental problem such as a dirty IAC or dirty throttle body or some other air/fuel issue.

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Vacuum leak is my first guess. check all those hoses to make sure they are on and not cracked.....second has to do with how my 09 impreza reacts to having the computer reset. It seems to need some run time before it gets all its settings in check.

 

I didn't think vacuum since I was pulling the trans and didn't mess with any of the lines, but worth a check.

 

 

 

This is interesting, hadn't considered that at all.  I'm using the neutral switch that came on the replacement trans, but I still have the original so may swap that out and see what happens.

 

 

 

Hoses on the intake tube loose. Intake tube clamps loose. Airbox not assembled properly.

 

The 99 and up also tend to have some issues with re-learning idle settings after the battey has been disconnected. Check over all of the wiring and hoses you had unhooked during the work and make sure that's all connected properly first. If all of that checks out, disconnect the battery for about 15 minutes.

Reconnect battey and start the engine, let it idle on its own. DO NOT TOUCH THE GAS PEDAL to keep idle speed up. If the engine stalls, turn the key off, restart it, and just let it idle so the computer can figure itself out.

Allow it to idle until the cooling fans cycle on then back off. If its a cool day this might take a while.

Once the cooling fans turn off, turn the engine off and let it cool for about an hour.

After an hour, restart the engine, let it idle for about 10 minutes, again no gas pedal. If it stalls just restart it. After 10 minutes take it for a drive, about 15-20 minutes in a residential area. Park it, turn the engine off, wait a minute or so, restart and take it for a drive on the highway where you can sustain at least 45 mph speed for 10 minutes or so, then drive it home park it and let it cool off. If you follow that correctly the ECU should relearn proper fuel trims for idle and cruise and you shouldn't have any trouble after that.

 

If you still have the problem after that, something was overlooked like a loose vacuum hose or you have a coincidental problem such as a dirty IAC or dirty throttle body or some other air/fuel issue.

 

Interesting.  When I was taking everything apart, the hose clamp for the intake boot on the throttle body was completely loose.  There were cracks on one of the hoses for the PCV system that I mentioned earlier (the one I couldn't find) and a missing clamp on another.  I'm veering away from coincidental problems as it ran beautifully before I took it apart.  Not to say those can't happen, but want to eliminate "operator error" first.

 

I've been driving it and it doesn't stall anymore, but the idle will still be sporadically rough and the engine check light hasn't gone away.

 

Fairtax,

 

I've checked over all the connections and vacuum lines and everything seems to be in order.  I'll try out your ECU reset and see if that does it.

 

Thanks everybody!

Will-

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Vacuum lines can crack, harden, split, stretch, get soft and mushy, etc. Heat and contaminants are main causes. Visual inspections mean absolutely NOTHING. 

 

On really small nipples, vacuum hose can harden over the nipple from transferred heat, but be soft and pliable 1/4" beyond the nipple. If 1psi of water was going through the hose, it'd leak. If a vacuum can't be maintained, it'll affect the engine's ability to run smoothly.

 

My Legacy is older, but was 100% stock under the hood when purchased. I had erratic idling at one point. So I went to parts store, and bought about 5 feet of vacuum lines that matched the ID of the hoses on the car, and systematically replaced every hose, one at a time. Only do one at a time as it's too easy to either miss something or connect wrong in some locations. Be sure to also replace EVAP hose under the hood as well as any sensors under the intake runners, etc. If engine has a PCV system, replace those as well. 

 

On mine, I think there was an area that served as a junction, and they used an odd jump-size in diameter (like going from 1/4" to 5/16" or similar) and I had to get creative buy wetting the inside of the hose and using elbow grease and a small ziptie for added security. Do NOT pull hoses that are tight as you risk breaking nipples. Score the hose with a razor and twist lightly, it'll pop off.

 

I noticed my engine ran a tad stronger and felt more responsive after doing mine, and idle smoothed out. Even if it doesn't fix the issue, it'll eliminate quite a few unknowns. You also might want to inspect any grounds near the firewall around/on the trans, as well as connectors. It's possible something has corrosion and was bumped, and is causing erratic running issues.

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Vacuum lines can crack, harden, split, stretch, get soft and mushy, etc. Heat and contaminants are main causes. Visual inspections mean absolutely NOTHING. 

 

On really small nipples, vacuum hose can harden over the nipple from transferred heat, but be soft and pliable 1/4" beyond the nipple. If 1psi of water was going through the hose, it'd leak. If a vacuum can't be maintained, it'll affect the engine's ability to run smoothly.

 

My Legacy is older, but was 100% stock under the hood when purchased. I had erratic idling at one point. So I went to parts store, and bought about 5 feet of vacuum lines that matched the ID of the hoses on the car, and systematically replaced every hose, one at a time. Only do one at a time as it's too easy to either miss something or connect wrong in some locations. Be sure to also replace EVAP hose under the hood as well as any sensors under the intake runners, etc. If engine has a PCV system, replace those as well. 

 

On mine, I think there was an area that served as a junction, and they used an odd jump-size in diameter (like going from 1/4" to 5/16" or similar) and I had to get creative buy wetting the inside of the hose and using elbow grease and a small ziptie for added security. Do NOT pull hoses that are tight as you risk breaking nipples. Score the hose with a razor and twist lightly, it'll pop off.

 

I noticed my engine ran a tad stronger and felt more responsive after doing mine, and idle smoothed out. Even if it doesn't fix the issue, it'll eliminate quite a few unknowns. You also might want to inspect any grounds near the firewall around/on the trans, as well as connectors. It's possible something has corrosion and was bumped, and is causing erratic running issues.

 

 

Good advice, thanks.  I really should do this as all the rubber under the hood is original and I'm sure is ready to be replaced.  I'm kind of running on the "it was fine before I fucked with it" principle, but it could easily be something I tweaked/cracked that I didn't notice during the process.

 

I can say that all the grounds I cleaned off on both ends while I was doing the trans swap, I'm hip to that one.

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