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Discussion Starter · #1 ·
Several months ago, I bought a 2002 Outback Sport with ~98k miles. Around 105k, the exhaust rusted out and broke at the muffler (damn PA winters). Rather than spending $130 on the OEM replacement muffler only, I bought a cat back exhaust off of an 02 WRX with 30k miles from a guy for $40, and I paid my mechanic $90 to install it (which had to be welded because the flanges didn’t line up correctly, and the size jumped from 2” to 2.5” at the flange).

Since I was increasing the size of the exhaust, I also decided to do a cheap mod to the intake that I saw on rs25.com. Basically, I removed the stock intake back to the elbow on the airbox and installed a Ganzflow style intake tube made for a 94 accord, which fits almost perfectly. I also bought a drop-in K&N filter that is installed in the factory airbox.

After all this, I definitely notice some more low-end power (not to mention the nice gurgle from the exhaust). However, every once in a while, it feels like the engine misfires. It happens most often when 1) I am going moderately slow at low RPMs (1000 to 1500) and then hit the gas suddenly or 2) when I just punch it. It doesn’t do it all the time. Sometimes it just takes off no problem. But other times, it hesitates and sputters a few times before taking off. It will also sputter periodically somewhat as I continue to accelerate with the pedal to the floor. I did notice that it doesn’t do this if I run higher octane fuel (89+).

I know just enough about cars to make me dangerous, but not enough to know exactly what to do here. I have some ideas based on what I can see. Should I change the fuel mixture? More rich? Less rich? How do I do that? How much should it cost? Is it something as simple as changing the spark plug gap or buying different plugs altogether? I’m trying to figure out if there’s something that I can do to fix the problem without the need to run premium fuel.

Any help is appreciated.
 

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2010 Forester
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TPS= throttle position sensor

To adjust is not fun and its best with 2 people. But you basically need a mulitmeter to hook up to your ECU and then (insert wrench size here) to adjust the actual sensor.

I have the data at home for the RS and I'm gonna assume that its the same. I'll edit once I'm home with the actual data. But you adjust the sensor based on your readings and it changes how rich/lean you run.

Also... Maybe check your valve lash...

And... If you're running rich (see buildup by your exhaust on your bumper) that's fine, if your exhaust is dry then you're lean and I would adjust your TPS then...

If you can get a code reader I would see what they are. They should be like 1001, 1002, 1003, 1004 for a misfire. That would be greatly appreciated.
 

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What's the TPS sensor? Would I get a CEL if that's the problem?

So what are the basics then?
The TPS sits on the other end of the throttle plate shaft (directly across where the throttle cable would hook up to)

My TPS was bad and I had no CEL. A misfire would definitely throw a code though.
 

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Discussion Starter · #6 ·
TPS= throttle position sensor

To adjust is not fun and its best with 2 people. But you basically need a mulitmeter to hook up to your ECU and then (insert wrench size here) to adjust the actual sensor.

I have the data at home for the RS and I'm gonna assume that its the same. I'll edit once I'm home with the actual data. But you adjust the sensor based on your readings and it changes how rich/lean you run.

Also... Maybe check your valve lash...

And... If you're running rich (see buildup by your exhaust on your bumper) that's fine, if your exhaust is dry then you're lean and I would adjust your TPS then...

If you can get a code reader I would see what they are. They should be like 1001, 1002, 1003, 1004 for a misfire. That would be greatly appreciated.

I have a multimeter. How do I know if I need to adjust the TPS and what to adjust it to? Do you have the data you were talking about?

I haven't been running it long enough with the current setup to notice any buildup at the exhaust.

If the fuel mixture is bad, would I get the codes without a CEL? If so, I'll scan it and see what it says.

BTW, forgot to mention that it also sputters sometimes when I'm idling. Like I said, it doesn't seem to do this when I use high octane fuel, which tells me it has something to do with the fuel or ignition. Since the plugs and wires are good, could it have anything to do with the gap? If not, I'm just going to assume that it's the fuel ratio.
 

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Discussion Starter · #7 ·
The TPS sits on the other end of the throttle plate shaft (directly across where the throttle cable would hook up to)

My TPS was bad and I had no CEL. A misfire would definitely throw a code though.

Thanks for the info. It may not actually be a misfire in the sense that the plug is not firing or the timing is off. It just feels like a misfire. Could just be poor combustion due to the fuel mixture. That's what I'm trying to figure out.
 

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2010 Forester
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Reserved for home

EDIT: Sorry, I drank WAY too much last night and didnt get home til late, and I passed out... Heres the info I was going to give you:

Just so you know what is where...


Using your mulitmeter you need to check the TPS for these numbers:


This is the connectors at the actual ECU, so you wanna look for the one in the middle (28 pin, use the top rows as a reference)


Follow these wiring diagrams to show the colors of the wire as well as where they are on both sets of connectors:
This one shows it at the TPS


And this one at the ECU 28 Pin
 

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2010 Forester
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All the data you need to check the TPS is up, but I would start basic as well...

Could be your fuel filter. I would run like shit at regular grade gas, but once I bumped up to mid grade it was better. So you might just have to run a higher octane. Check your codes and see what if anything is on there...
 

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Discussion Starter · #11 ·
Reserved for home

EDIT: Sorry, I drank WAY too much last night and didnt get home til late, and I passed out... Heres the info I was going to give you:

Just so you know what is where...


Using your mulitmeter you need to check the TPS for these numbers:


This is the connectors at the actual ECU, so you wanna look for the one in the middle (28 pin, use the top rows as a reference)


Follow these wiring diagrams to show the colors of the wire as well as where they are on both sets of connectors:
This one shows it at the TPS


And this one at the ECU 28 Pin
Is there supposed to be an attachment to this? Seems like I'm missing something. I don't see any of the number's you're referencing...maybe it's my firewall at work.

I changed the fuel filter shortly after I bought it using the basic OEM replacement. If this gets too complicated, I'll just bite the bullet and use 89 octane. It's better for the car anyway.
 

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Discussion Starter · #13 · (Edited)
I haven't had a chance to do anything to try to fix the problem, but here's an update.

Got a CEL a couple of weeks ago. Scanned it an got a catalyst efficiency code (P0420). Disconnected the battery overnight and the light disappeared for a few hundred miles and just came back on last night as I had the pedal to the floor and the car was sputtering some as I described earlier. So, although the P0420 code could mean several things (exhaust leak, bad cat, bad sensor), I'm guessing that whatever is causing the misfiring (or whatever it is) is also causing the CEL.

It seems like the problem is getting worse. Either way, I'm probably going to try to go back to the stock intake and see if that fixes the problems.

Oh, and I also noticed that the exhaust definitely smells like gas. Too rich?

I'm still look for a solution from someone out there that allows me to keep the moded intake and eliminates the misfiring/sputtering. So, if you have one, let me know.
 
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