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Discussion Starter · #1 ·
Now that I finally have my engine running properly and not throwing any check engine lights, this issue has become more obvious to me. When the engine is idling, especially after a cold start, when I hit the throttle it will dive down in revs before rebounding and revving up like it should. It is never enough to stall, but it makes it difficult to start in first gear, especially with someone who isn't amazing driving stick (yet). I am thinking maybe the TPS? My MAF is brand new so I do not think it is that, and the wires on the TPS are switched like they are supposed to be. I do have a leak in my exhaust I am attempting to figure out and fix, so maybe that is part of the problem as well? Any advice or troubleshooting welcome.
 

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The first step to troubleshoot this is use a scantool or scantool app with live data and check that the throttle position sensor reads about 10% at idle and about 90% at wide open throttle. You can also check that your MAF reads about 3g/s or something like that at warm idle. Here's a video showing how you to configure and use a scantool app to troubleshoot issues on a 2zz or 1zz.

 

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This! Also, how many miles have you driven it. My 2ZZ always has odd tip in until I drive it well more than 50 miles on the OEM ECU. Probably because of a different intake configuration.
 

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Discussion Starter · #4 ·
I have only driven maybe 15 miles or so on it, and from what I remember I already checked all the values and they seemed normal. So what you are saying is that the ECU has a kind of learning period to get through and it may get better?
 

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Yeah this is normal as the swap intakes don't quite duplicate the stock one for airflow especially at low load. There is a Cobb intake for Subaru some people use that works a bit better, but honestly just put some miles on it and this tip in issue will get much better. Which intake do you have?
 

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Discussion Starter · #6 ·
I found someone selling an intake that was custom made on ebay, but it's the proper inner diameter just a straight tube about a foot long that I have a right angle silicone tube going onto the throttle body. It also has some honeycomb in the front of it to try and smooth out the incoming air. If my battery dies and the ecu resets, will it get worse again until it relearns?
 

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The first step to troubleshoot this is use a scantool or scantool app with live data and check that the throttle position sensor reads about 10% at idle and about 90% at wide open throttle. You can also check that your MAF reads about 3g/s or something like that at warm idle. Here's a video showing how you to configure and use a scantool app to troubleshoot issues on a 2zz or 1zz.

mine reads about 12% and 74% - would that be problematic?
 

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I don't think this will cause any drivability issue or performance issue. But 74% is on the low side. Check if there is anything interfering. Carpet/floormat? Then check on the throttle body side. Does the throttle butterfly valve itself or the cam that the cable attaches have more range of motion than the cable is producing. To check this use a cinder block or something else equally ehavy to hold the pedal to the floor, and check if the cam/butterfly is at its maximum rotation, or more rotation is available if you turn it manually producing slack in the cable. Also check what is thie position of the cable with no pedal - is there slack that has to be taken up before the cam rotates? Basically suggesting that you take a close look at it to identify any potential issue. Nobody really knows what this ecu does with the throttle position. There is definitely a tip-in behavior based on the rate of motion of the pedal. And there is also a use of the tps for fueling while in limp mode i.e with the MAF unplugged or non-functional. The throttle position also determines transition from closed loop to open loop fueling that I believe happens at about 30% throttle opening - would have to double check this. Past that point it does not really matter what the throttle position reads, except for acceleration enrichment. Oh god I just produced a nonsense wall of words again.
 
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