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Old 06-13-2022, 04:10 PM   #1
Rigid80sMTB
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Default EJ22 rough idle, hesitation, high ltft...no vacuum leaks?

So my '96 Impreza L has developed this extremely annoying issue in the past year where it has a rough, bouncy idle and hesitation when accelerating from a stop. And while trying to hold the throttle steady at lower rpms, say 2k or less, the rpms bounce up and down slightly making the car jerk back and forth. I have read every single related thread I can find and have yet to find a solution.

No CEL codes.

Here's everything I've replaced recently, with no improvement:

- MAF
- PCV
- TPS (adjusted to 0.5v)
- Front O2 (voltage looks normal)
- Knock sensor (twice)
- Spark plugs
- Spark plug wires
- Fuel filter
- Fuel pump
- Exhaust manifold gaskets
- Timing belt kit (have checked timing multiple times - marks line up perfect and tooth count is correct)
- Installed 2 new grounds and cleaned all original ones

I recently got an OBD2 scanner, and I think I've found at least part of the issue. My long term fuel trims at idle sit around 23%. When I'm accelerating it goes down quite a bit, to like 5% or less. So this would indicate a vacuum leak right? Well...I have smoke tested for vacuum leaks more times than I can count now and have yet to find any. So what else could possibly cause this?
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Last edited by Rigid80sMTB; 06-13-2022 at 04:17 PM.
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Old 06-13-2022, 10:32 PM   #2
Wannabe WRX
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Have you had the car re-learn idle?
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Old 06-14-2022, 10:19 AM   #3
Rigid80sMTB
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Quote:
Originally Posted by Wannabe WRX View Post
Have you had the car re-learn idle?
I haven't recently. I tried this a few times in the past and it never seemed to make a difference.

Also, something new happened yesterday. I went to start the car after work and it had to crank for like 5+ seconds to start. Never done this before. Beginning to wonder if it's a bad crank sensor.

For a while now I've had to turn the key multiple times to start the car. Rarely it will crank over first try but sometimes I have to turn the key like 20 times before it actually engages the starter. I assumed this was a worn out ignition switch or starter solenoid but maybe not?
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Old 06-14-2022, 01:12 PM   #4
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a 96 doesn't need to re-learn idle, it's a cable driven throttle. Look into the fuel pressure regulator. inspect the intake manifold gaskets for leaks. Simply removing the manifold might tear them up enough to necessitate replacement. Also, check the throttle cable. It needs just a little slack. Too tight will mess with idle, too loose and you won't get to full throttle.

As for your starting, that sounds like a worn ignition switch. You can always check for 12v on the starter trigger when you turn the key to see if operation is consistent.
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Old 06-20-2022, 10:51 AM   #5
Rigid80sMTB
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Okay well it's probably going to be a while before this specific issue is diagnosed because I'm pretty sure my 4eat just decided to kill itself. It now shifts into neutral on it's own above 50 mph. Seems to have the right amount of trans fluid. Still nice and pink and doesn't smell burnt so idk. These old 4eats are truly terrible.
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Old 12-08-2022, 10:09 AM   #6
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My transmission decided to start working again (prob not for long, hoping to manual swap soon) so I'd still like to try and fix this.

Basically I need to figure out what is causing my ridiculously high long term fuel trim (15-20%) at idle. Because that is without a doubt causing issues.

I took it out for a drive last night with my obd2 scanner just to confirm that my sensors are working properly. CTS, TPS, MAF, and O2 all seem to be working as they should.

Quote:
Originally Posted by yarrgh View Post
Look into the fuel pressure regulator. inspect the intake manifold gaskets for leaks. Simply removing the manifold might tear them up enough to necessitate replacement. Also, check the throttle cable. It needs just a little slack. Too tight will mess with idle, too loose and you won't get to full throttle.
I've adjusted the throttle cable, it has just the right amount of slack. Not too tight. I've never removed the intake manifold so I'd be surprised if it suddenly started leaking on it's own.

I was also thinking fuel pressure regulator especially since the car will occasionally take a bit longer than usual to start. Which I'm assuming means its losing fuel pressure as it sits. Seems to be completely random though. Not sure what else it could be because I've replaced damn near everything else. Clogged injector or something possibly?

Last edited by Rigid80sMTB; 12-08-2022 at 10:21 AM.
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Old 12-08-2022, 10:53 AM   #7
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Quote:
Originally Posted by Rigid80sMTB View Post
My transmission decided to start working again (prob not for long, hoping to manual swap soon) so I'd still like to try and fix this.

Basically I need to figure out what is causing my ridiculously high long term fuel trim (15-20%) at idle. Because that is without a doubt causing issues.

I took it out for a drive last night with my obd2 scanner just to confirm that my sensors are working properly. CTS, TPS, MAF, and O2 all seem to be working as they should.



I've adjusted the throttle cable, it has just the right amount of slack. Not too tight. I've never removed the intake manifold so I'd be surprised if it suddenly started leaking on it's own.

I was also thinking fuel pressure regulator especially since the car will occasionally take a bit longer than usual to start. Which I'm assuming means its losing fuel pressure as it sits. Seems to be completely random though. Not sure what else it could be because I've replaced damn near everything else. Clogged injector or something possibly?
-Do a smoke test
-replace all hoses and vacuum lines
-replace intake manifold gaskets
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Old 12-08-2022, 11:01 AM   #8
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Quote:
Originally Posted by blurred View Post
-Do a smoke test
-replace all hoses and vacuum lines
-replace intake manifold gaskets
I have smoke tested this thing more times than I can count lol. If there's any vacuum leaks they're not showing up from a smoke test. I'll prob go ahead and order some intake manifold gaskets, it looks to be a way easier job than I thought.
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Old 12-08-2022, 07:41 PM   #9
Elbert Bass
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Quote:
Originally Posted by Rigid80sMTB View Post
I have smoke tested this thing more times than I can count lol. If there's any vacuum leaks they're not showing up from a smoke test. I'll prob go ahead and order some intake manifold gaskets, it looks to be a way easier job than I thought.
You're searching using pressure - boost leak test. That's great for turbo cars that pressurize the intake. Vacuum leaks occur under negative pressure. That means it may not leak under pressure. Run engine at idle, spray small, short shots of carb or brake cleaner in different areas. When RPM increases or fuel trim starts to drop you are getting near.
On the other side you could have a leaking exhaust manifold gasket or crack before the A/F sensor. That allows fresh air in the exhaust and dilutes the exhaust causing the A/F sensor to read too lean.
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Old 12-10-2022, 04:49 PM   #10
Rigid80sMTB
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Ok so I replaced the intake manifold gaskets, and this of course made no difference whatsoever. Long term fuel trims are still just as high as before. Doesn't run any better.

Quote:
Originally Posted by Elbert Bass View Post
You're searching using pressure - boost leak test. That's great for turbo cars that pressurize the intake. Vacuum leaks occur under negative pressure. That means it may not leak under pressure. Run engine at idle, spray small, short shots of carb or brake cleaner in different areas. When RPM increases or fuel trim starts to drop you are getting near.
On the other side you could have a leaking exhaust manifold gasket or crack before the A/F sensor. That allows fresh air in the exhaust and dilutes the exhaust causing the A/F sensor to read too lean.
I tried checking for leaks with brake cleaner earlier today and didn't find anything. I recently replaced the exhaust manifold gaskets thinking that may be it. Made no difference.
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Old 12-13-2022, 10:55 AM   #11
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Couple things I think I need to check:

- Fuel injectors. I believe the way you'd usually check these is by unplugging them one by one. Not sure how well this will work though because I don't think I have a completely toasted injector. Maybe just one that's clogged a bit.

- Timing. I changed the timing belt a couple years ago and I feel like this may have started around the same time? Not entirely sure. I have checked the timing multiple times since and everything seems to be lined up perfectly. BUT! Here's the thing - I recently acquired a '98 impreza wagon. It ran pretty smooth when I got it. Then I replaced the timing belt and guess what. Annoying lumpy idle, just like my '96. So I get back in there and check. Tooth count is correct and all the timing marks are lined up. So wtf? Started thinking and I remembered that before I pulled off the original timing belt, the passenger side cam was actually slightly left of the timing mark with everything else lined up. So I readjusted my belt so that it was just like before. Passenger* side cam lined up just slightly to the left of the timing cover mark, crank and driver's side cam lined up perfectly. Got it all back together and guess what? It idles great now. This leads me to believe that the timing marks on these things aren't always completely accurate. Not sure this would explain my insane fuel trims though.

Last edited by Rigid80sMTB; 12-13-2022 at 03:52 PM.
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Old 12-13-2022, 09:35 PM   #12
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Took a vid earlier to see if I could hear any exhaust leaks from the header. I don't hear anything out of the ordinary but if anyone else wants to check, here's the video:

imgur.com/d5hCGWk

Also I swear it doesn't leak oil as bad as it looks lol.
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