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Old 01-27-2012, 10:07 PM   #1
klarowe
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Default 2004 STI Possible TPS issue

The STI has been running a little odd lately and I'm trying to get some opinions. For a little while now its had a very slight rough / hunting idle... almost surging so to speak. Hasn't really bothered me so I haven't been working about it. But within the past couple weeks I've been having a hesitation issue. At cruising speed its a very consistent but VERY light miss but its barely noticeable. The big issue is when I try to get on it even slightly the miss is amplified to where in1st gear it will be as if I just completely let off the throttle and it just falls on its face for a second and then kicks back in. At first I though plugs so I put new plugs in and it didn't change anything. But then I noticed that it seems to be linked more to pedal / throttle position than RPM related, so I started looking into the TPS. I had to pull the TMIC off anyways to also look at my methanol flow sensor which hasn't been reading right and when I had just the ignition on (obviously, the car wasn't running), there was a higher pitched almost buzzing noise coming from the throttle controller... which as far as I know is also the TPS and idle control. I'm assuming this buzzing is not normal and that would explain both the hesitation and the idle issue... but before I go dropping $160+ on a new TPS I'd like to be as sure as possible.

So anyone have any opinions on the matter?

Thanks in advance.
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Old 01-27-2012, 10:49 PM   #2
jdblock
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O2 sensor going bad?
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Old 01-27-2012, 10:52 PM   #3
jdblock
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And the TPS uses the same sensor as is on TGVs, you can find a TGV sensor for much cheaper from someone who has done deletes.
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Old 01-27-2012, 11:00 PM   #4
klarowe
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I have the TGV delete done... don't think I have the sensor still though.

But now here is another question... the buzzing is coming for the throttle control module. I assumed the TPS was a part of that since the only other sensor I saw was mounted on top of the throttle body and I don't see how it would be able to sense the throttle position...
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Old 01-27-2012, 11:35 PM   #5
jdblock
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The tps is on the gas pedal in the car, since it's DBW. I would look at the O2 sensor first though.
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Old 01-28-2012, 01:39 PM   #6
klarowe
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I don't think its the O2 sensor b/c I have a wideband o2 setup that is not connected into the cars computer. Unless it is the downstream o2, but that is usually only used as an emissions check.
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Old 01-28-2012, 04:47 PM   #7
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Get a good volt meter. There should be 3 wire one ground one power and one signal on the tps connector. Find which is which and unplug it. Using the volt meter ground the black lead to a good ground and the red/positive lead to the signal on the tps and slowly move your throttle all the way open and your readings should increase slowly. You have to do this with key in the ignition to the on position NOT with the motor running. Readings should be .05 closed throttle to 4.5 ish at wot. Watch for sudden voltage glitches. I can't recall if you can do this if its a electric throttle versus a cable. But worth a shot I guess. And is there and mil light with the car running the way it is?
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Old 01-28-2012, 09:49 PM   #8
klarowe
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Quick update. Did a little more work / diagnosis and decided to hook up the code reader in hopes of finding something... even though the MIL was not on. And I lucked out a bit. I had 3 codes; TPS high input, IAT high input, and MAF high input. The MAF and possibly the IAT could be from when I was working on it. To test the flow sensor for the meth I was disconnecting / reconnecting the MAF with the ignition on.. which I'm sure was throwing **** for a loop. Not sure why the IAT was going off, but I was messing with just about everything near the TMIC. However I never once messed with the TPS so there is no reason that should have been tripped. I cleared everything and I'll recheck the codes after a little while and see if it comes back on.

Subaru_sti_steve: Thanks! I am very good when it comes to 12volts and using a DMM... I just didn't know exactly what I needed to test for. I will give that a shot tomorrow and see what I come up with. But you say to unplug it.... if I unplug it then the TPS won't have a 12v input and I won't get any readings??? I will have to test it with the TPS connected, correct?
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Old 01-29-2012, 02:57 AM   #9
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Sorry I meant with it plugged in probe it
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Old 01-29-2012, 05:50 PM   #10
klarowe
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Here are the results of the TPS test. I had 6 wires at the switch, not just 3.
From the left side of the plug (connector on top
Red/black - tested ground regardless of key position or throttle position
Red - showed 1.05v at resting throttle and SMOOTHLY increased to 3.72v at WOT
Yellow - tested ground regardless of key or throttle position.
Lt. Green - 5v constant with key on
Dk Blue - showed 1.18v at resting throttle and SMOOTHLY increased to 3.84v at WOT
Lt Blue - 5v constant with key on

Both wires that changed with throttle position increased smoothly. It was tough to do through slowly, but I was able to adjust it in .02v - .04v increments.

So now I have no idea what is going on. And I rechecked for codes and brought up nothing. I'm heading out of town for a couple days tomorrow and have a rental car for the trip so I won't be needing it (or be able to look further into it). But when I get back I may just have to drive it until it throws a code and keep my code reader on me for when it does.
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Old 01-29-2012, 06:06 PM   #11
klarowe
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I did some Google searching and found an article that described the Subaru DBW system in depth. Apparently it uses a redundant signal as a "back-up" which would explain why I had doubles of everything. So from what I can tell, other than a slight difference in voltage on the "position" wire (1.05v-3.72v vs 1.18v - 3.84v) everything seems ok. When I get back I will test the wires at the actual module on the TB and see what I'm getting there.
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Old 02-01-2012, 06:55 AM   #12
klarowe
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Update: I started up the car this morning and the MIL immediately came on AND the cruise control light was flashing. I checked the DCCD to make sure it wasn't related and the DCCD was working fine. I plugged in my scanner and got a P0172 System too rich (Bank 1) and the same code but PENDING. Not quite sure how it knows the system is too rich because the upstream O2 sensor is my wideband and it is not connected to the ECU at all (as far as I know). I'm starting to wonder if there is a dead spot in the tune... but I could be way off.
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Old 02-04-2013, 03:47 AM   #13
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Have the same issue on my 04 STi. I eventually swapped to a used throttle body I bought off a nasioc member off an 06. Only difference was a vacuum hose of some sort that I cut right off. Code hasn't come back until recently. It will have that same "surge" like failure especially after commutes. Hopefully you can figure something since I'm stumped.
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Old 02-04-2013, 08:29 AM   #14
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Quote:
Originally Posted by klarowe View Post
Update: I started up the car this morning and the MIL immediately came on AND the cruise control light was flashing. I checked the DCCD to make sure it wasn't related and the DCCD was working fine. I plugged in my scanner and got a P0172 System too rich (Bank 1) and the same code but PENDING. Not quite sure how it knows the system is too rich because the upstream O2 sensor is my wideband and it is not connected to the ECU at all (as far as I know). I'm starting to wonder if there is a dead spot in the tune... but I could be way off.
Are you saying you removed your upstream O2 and put your WB there? Cause if you did, that's your problem right there.
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