Welcome to the North American Subaru Impreza Owners Club Monday July 24, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 06-02-2017, 08:59 PM   #1
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default Troubleshooting why it idles this way

See if anyone can input on this :

1997 Impreza obs.
Auto trans. 2.2 engine.
Location: New Mexico

Recently replaced:
MAF sensor
Fuel pump
Fuel filter
Air filter
Replaced a year ago or so,
Spark plugs.

Last time pumped gas 1 week ago with fuel grade "86".

Issue:
When approaching normal temperature at idle
It acting like it wants to turn off.
When replaced MAF Seemed so make it a bit better. It hesitates on acceleration when under load. Before replacing the MAF it would turn off after 5 minutes. No CEL codes are on. Which makes it more harder to diagnose.

Next step in replacing
Spark plug wires,
Coil pack,
TPS sensor

Any other ideas on what to replace next to solve this problem?

Thanks.
* Registered users of the site do not see these ads.

Last edited by Boxer1687; 06-02-2017 at 09:56 PM.
Boxer1687 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 06-03-2017, 10:24 AM   #2
Elbert Bass
Scooby Specialist
 
Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
Default

Do you see black smoke from exhaust after it warms up? Does your scan tool show data? What is the temp sensor reading when it's warmed up?

If you're just throwing parts at it I would try an engine coolant sensor next. Double check none of the hoses on the intake are loose, cracked, or have holes.
Elbert Bass is offline   Reply With Quote
Old 06-03-2017, 12:15 PM   #3
CarmelValleyWRX
Scooby Newbie
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

could be leaks from air intake to throttle body, or stuck idle air control valve.
CarmelValleyWRX is offline   Reply With Quote
Old 06-03-2017, 04:49 PM   #4
Charlie-III
Scooby Guru
 
Member#: 30669
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
Vehicle:
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

Default

Along with this, can you read LTFT's? If so, what are they?
Hopefully you have a scanner that can read realtime data, then you can watch ECT (engine coolant temp) and other bits while it's running.
Charlie-III is offline   Reply With Quote
Old 06-03-2017, 11:52 PM   #5
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default Troubleshooting why it idles this way

Quote:
Originally Posted by Elbert Bass View Post
Do you see black smoke from exhaust after it warms up? Does your scan tool show data? What is the temp sensor reading when it's warmed up?

If you're just throwing parts at it I would try an engine coolant sensor next. Double check none of the hoses on the intake are loose, cracked, or have holes.


Thanks for your reply.

Scan tool only shows if the CEL is on. Temp In normal conditions when car is fully warm.
Thanks for the tip about the Engine Copland sensor. I'll try that.

Thanks again all.
Boxer1687 is offline   Reply With Quote
Old 06-04-2017, 10:12 AM   #6
Elbert Bass
Scooby Specialist
 
Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
Default

Quote:
Originally Posted by Boxer1687 View Post
Thanks for your reply.

Scan tool only shows if the CEL is on. Temp In normal conditions when car is fully warm.
Thanks for the tip about the Engine Copland sensor. I'll try that.

Thanks again all.
Charlie-III and I are talking about the sensor for the ECM, not the gauge. Those are two different sensors. Seeing the fuel trims Charlie-III mentioned would be a big help too.
Elbert Bass is offline   Reply With Quote
Old 06-04-2017, 02:11 PM   #7
CarmelValleyWRX
Scooby Newbie
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

i had a 1996 legacy with the 2.2l. it seemed to have a really basic ECU which didnt have much info.
CarmelValleyWRX is offline   Reply With Quote
Old 06-05-2017, 01:01 PM   #8
v2rocket_aka944
Scooby Newbie
 
Member#: 408701
Join Date: Dec 2014
Default

obd scanner should show ST and LTFT even if no CEL.

i agree with the "check the coolant temp sensor" above.
thinking it's running lean (weak power, or maybe not enough gas to run at all) especially in a "warm" place like NM...
v2rocket_aka944 is offline   Reply With Quote
Old 06-06-2017, 12:05 AM   #9
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default

Quote:
Originally Posted by v2rocket_aka944 View Post
obd scanner should show ST and LTFT even if no CEL.

i agree with the "check the coolant temp sensor" above.
thinking it's running lean (weak power, or maybe not enough gas to run at all) especially in a "warm" place like NM...


True. I have a scan reader on the way ordered.
Also I'm purchasing the coolant temp sensor now. The car is half tank. Just replaced fuel pump and filter as well.

Remember I said it starts off no problem. Only when the temp gauge starts showing that is running on normal temp is when it's starts stuttering.

(206k miles)
Boxer1687 is offline   Reply With Quote
Old 06-06-2017, 07:30 AM   #10
Elbert Bass
Scooby Specialist
 
Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
Default

Quote:
Originally Posted by Boxer1687 View Post
True. I have a scan reader on the way ordered.
Also I'm purchasing the coolant temp sensor now. The car is half tank. Just replaced fuel pump and filter as well.

Remember I said it starts off no problem. Only when the temp gauge starts showing that is running on normal temp is when it's starts stuttering.

(206k miles)
That's why coolant temp sensor is suspect. If it is faulty it is most likely open circuit. If it is open circuit the ECU sees minus 40 degrees (live data will show you that).

When a cold/cool engine starts it needs extra fuel to warm up and is running on a preprogrammed map based on temp. Problem is once engine is warm it no longer needs that extra fuel, but a faulty temp sensor can make it think it's still cold. That enriches the A/F mixture and runs too rich causing stalling, stumbling, etc. Because the ECM thinks it is cold it will not go in closed loop. Closed loop is where the ECM switches from that preprogrammed map and uses the A/F and O2 sensors to determine fuel ratios. That's why I asked about black smoke - that indicates it is too rich. Those fuel trims (again live data will show those) will also tell you if it is too rich.

v2rocket_aka944: Temp sensor generally won't cause a lean condition because they usually fail open circuit. Automotive applications use negative temperature coefficient sensors - resistance decreases as temperature increases. That ensures that if the sensor fails it looks cold and you can at least get the vehicle started initially. Later model systems will tell you the sensor has a fault, but not these earlier ECMs.
Elbert Bass is offline   Reply With Quote
Old 06-06-2017, 11:52 AM   #11
v2rocket_aka944
Scooby Newbie
 
Member#: 408701
Join Date: Dec 2014
Default

In my non-Subaru car a screwy ECT sensor can cause a bad lean problem - it's happened on my car before and is a common issue. Don't know what goes bad in them (sensor is almost identical in design to the Subaru part).

Car will start fine cold (getting proper cold enrichment) but as coolant warms up the sensor will over-state the temperature and force ECU to lean out. Car will be really soft on power. Ever tried to pass someone on the highway with a 17:1 AFR?
v2rocket_aka944 is offline   Reply With Quote
Old 06-06-2017, 08:11 PM   #12
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default Troubleshooting why it idles this way

No black smoke at all. But it can still be the ect just like you explained. All I'm doing now is waiting for parts to arrive. And waiting on the new obd 2 scanner that's on the way. Can't wait to see what the results are. Learning experience. What kind of normal reading am I suppose to read on the scanner? Or is it wise for me to read it off my other car (98 Impreza obs manual trans) will it read the same or will it read different because of the trans difference? ( auto trans having to be connected to coolant lines)
Thank you Elbert. The specific explanation so I can understand how the system works.

V2rocket: when I was looking at this sensor online, it fits a variety of vehicles. So it might work similar to what you said.
Boxer1687 is offline   Reply With Quote
Old 06-07-2017, 12:51 AM   #13
Charlie-III
Scooby Guru
 
Member#: 30669
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
Vehicle:
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

Default

When you start the car, ECT should be about ambient temp, when the fans come on, ECT should be about 200*F/100*C. If the sensor is bad (either one) they will be nowhere near either value.
So, watch the gauge in the cluster as well,as what the realtime data shows in the scanner.
Charlie-III is offline   Reply With Quote
Old 06-07-2017, 04:58 AM   #14
soundquest
Scooby Newbie
 
Member#: 468926
Join Date: Jun 2017
Default

Quote:
Originally Posted by CarmelValleyWRX View Post
could be leaks from air intake to throttle body, or stuck idle air control valve.
Another vote for IAC valve (and ECT for that matter). I have had both produce anomalies when they went south (clogged rather in the case of IAC). IAC is super accessible -- would be a good idea to thoroughly clean it just to rule it out.
soundquest is offline   Reply With Quote
Old 06-07-2017, 11:55 AM   #15
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default

Quote:
Originally Posted by soundquest View Post
Another vote for IAC valve (and ECT for that matter). I have had both produce anomalies when they went south (clogged rather in the case of IAC). IAC is super accessible -- would be a good idea to thoroughly clean it just to rule it out.


Will do. Good advice. Would like to buy one if it is not working properly. They go from $70-400.
Only place I checked is on eBay so far. I'd rather clean it before buying it. Thanks.
Boxer1687 is offline   Reply With Quote
Old 06-10-2017, 03:40 PM   #16
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default Troubleshooting why it idles this way

Replaced coolant temp sensor.
Replaced IAC with a clean one.
Replaced the coolant that was lost while removing the IAC.
Cleaned the hoses connected to the air intake. (Clogged/dirty)

Same issue. Same symptoms.

Next steps:
Replace spark plug wires.
(Spark plugs checked, good. Have 20k since been replaced)
Ignition coil pack.
TPS (coming in later today)
Taking apart the throttle body to clean.

Any other ideas?? Please input.
Boxer1687 is offline   Reply With Quote
Old 06-25-2017, 04:58 PM   #17
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default Troubleshooting why it idles this way

Replaced coil pack,
Spark wires, cam sensor coil pack.

What would a mechanic would say if I take it in for a inspection to diagnose?

Fuel pressure regulator replacement?
Fuel injectors?

Still no CE code.
And a REAL live reader is too expensive for my budget right now.

Last edited by Boxer1687; 06-25-2017 at 05:16 PM.
Boxer1687 is offline   Reply With Quote
Old 06-26-2017, 08:10 PM   #18
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default Troubleshooting why it idles this way

Finally had the balls to drive this car. 20 miles round trip. No hesitation on accelerating on uphill so far. My wife says the same thing. But still idles rough and same problems that if I hold the pedal steady on idle on 3k or 2k rpm; the rpm lowers.
Tomorrow I'm going to work. About 55 miles there and 55 back. I hope I don't get stranded...

Before I replaced all the parts I mentioned. On idle it used to turn off on me once it reached normal temp. Now it doesn't. Does the ecm need to get used to all the parts installed?
Boxer1687 is offline   Reply With Quote
Old 06-27-2017, 07:41 AM   #19
Charlie-III
Scooby Guru
 
Member#: 30669
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
Vehicle:
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT

Default

Quote:
Originally Posted by Boxer1687 View Post
Finally had the balls to drive this car. 20 miles round trip. No hesitation on accelerating on uphill so far. My wife says the same thing. But still idles rough and same problems that if I hold the pedal steady on idle on 3k or 2k rpm; the rpm lowers.
Tomorrow I'm going to work. About 55 miles there and 55 back. I hope I don't get stranded...

Before I replaced all the parts I mentioned. On idle it used to turn off on me once it reached normal temp. Now it doesn't. Does the ecm need to get used to all the parts installed?
Ideally when doing a lot of work, clear the fine learning in the ECU. Either clear codes with a scanner, or (I never tried it but sounds like it may help) disconnect the battery and hold the 2 battery cables together for a minute or so.

What plugs did you put in? Hopefully NOT Bosch Platinum. NGK Platinum are fine, I usually just use NGK V-power.
Charlie-III is offline   Reply With Quote
Old 06-27-2017, 09:19 AM   #20
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default

Thanks for the responds. NGK V power.
Boxer1687 is offline   Reply With Quote
Old 06-27-2017, 09:23 AM   #21
Boxer1687
Scooby Newbie
 
Member#: 369969
Join Date: Oct 2013
Default

Quote:
Originally Posted by Charlie-III View Post
Ideally when doing a lot of work, clear the fine learning in the ECU. Either clear codes with a scanner, or (I never tried it but sounds like it may help) disconnect the battery and hold the 2 battery cables together for a minute or so.



What plugs did you put in? Hopefully NOT Bosch Platinum. NGK Platinum are fine, I usually just use NGK V-power.


Thanks for the response. Using NGK V power. Plugs are duralast.

Drove it today for a hour.
55-65 mph. For 55 miles. Up hills feel better than my 98 Impreza lol

Stopped for gas and put it on park. Idled smooth. When I turned it back on after filling it up with "88" grade gas (which is what I normally put on all my cars) it idles rough again. I'll try the battery trick. And no CE codes on. Thanks
Boxer1687 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 11:37 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2017 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.