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Old 11-24-2008, 10:38 PM   #1
qstarin
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Default 2k+ idle started after a clunk & bog + P1507 code

Last night I was on the highway doing 70 (3k rpm in 5th) for half an hour when I heard a fairly loud clunk in the engine bay immediately followed by a distinct change in the sound of the engine and a loss of power. Downshifted to 4th and it started running fine. Pulled into the first gas station and noticed the idle was pegged at 2k rpm and it has been since.

On the way home - a couple hours later - the car did the same thing - clunk then bog. This time I left it in 5th and blipped the throttle several times to no effect. After about 5 seconds it just went back to normal.

When I got home I pulled the codes and got the normal P1596 for my missing 4EAT but also got a P1507 for the IACV. Because the check engine light is always on due to the tranny code, the P1507 could have happened any time since the last ECU reset - which was almost exactly 72 hours before - so, I assume pretty safely that it occurred with the clunk & bog. I cleared it and the P1507 has not reappeared despite having the high idle.

Car is 2001 2.5RS mostly stock. SPt short ram air intake. Swapped the 4EAT out for a 5MT from 93 Legacy over a month ago - neutral safety switch wires are shorted and I have no vehicle speed sensor. Also, while doing the tranny swap I found a headgasket leak and had STi multilayer headgaskets put in by a friend.

Because of the tranny swap, I get some idle issues that include 2k rpm idling immediately after an ECU reset that goes away after 4 or 5 starts and stops (like, car on - drive - car off - repeat). Also, from time to time, the idle bumps up to 1200-1400 RPM until the car is restarted.

This high idle is different. It is pegged at 2k to 2.5k rpm and it is stuck. It's also been like this specifically since the weird clunk and bog last night.

Today I took the IACV out. It wasn't all that dirty and there were no chunks or anything in it - just some film. Nevertheless, I cleaned it thoroughly and reinstalled it - but it still idles high.

I looked around the engine bay and there are no apparent vacuum leaks audible or visible, but I will need to inspect the intake manifold more thoroughly in the daylight tomorrow. I doubt I'm going to find a leak, though. Throttle cables have appropriate slack in them.


Can anyone offer any suggestion as to what could've caused the weird clunk then bog on the highway that seems to have caused a P1507 cel to get thrown and a persistent high idle (despite no more P1507 code)?
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Old 12-25-2008, 03:14 AM   #2
qstarin
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STM

Default Another similar but different bog incident

So I had another bog incident.

I was cruising down the highway for like 45 minutes at 2500-3000 RPM in 5th.

Then I got the bog, but it didn't go away.

After several seconds I pushed in the clutch. The RPM's dropped and started bouncing between 1000 and 1500 RPM's. I couldn't get any power in any gear.

So I pulled over and shut off the car for a few minutes.

Checked the codes - P1507, P0507, P0301, P0302.

After a few minutes it started right back up. Had my normal high (2k) idle that I get after a ECU reset or clear.

Got another 20 min down the road and it did it again. Pulled over and shut it off for a few minutes. No codes.

Stopped at a gas station and threw a bottle of Heet in (someone suggested freezing fuel as a possibility).

Another 10-15 minutes down the road it did it again. I killed the car while rolling and restarted it after a couple seconds. Fired back up and got me the last 20 minutes home. Still no more codes. Still idling high, probably still from the ECU clear - should go away by tomorrow.


Any ideas?

This is too weird. I'm thinking maybe having my NSS switch shorted is screwing with my ECU. Maybe frozen gas. Maybe water temp sensor for the ECU (cause I occasionally get a slightly high little bit hunting idle?).

Known issues seem to confound diagnosing unknown issues. I never know what could be related to what. Erg.
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Old 12-25-2008, 12:01 PM   #3
chazly413
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Default

Fuel freezes reaallllyyy cold, so I don't think it's that. Maybe some water in your gas tank that's freezing?
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Old 12-25-2008, 02:00 PM   #4
qstarin
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Default

Yeah - sorry, bad choice of words.

Meant water in the tank or lines that's freezing, not the actual gas.

Does that even sound plausible, though, as a cause of my most recent symptoms? If it does, it still leaves me with the previous bogging unexplained (since it wasn't anywhere near as cold previously).


What really gets me is that the car only acts up on longer highway trips (45min+) and those are the worst times for it to break down!
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Old 12-25-2008, 02:28 PM   #5
Storm
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Normally, the lack of a VSS signal will put the car in limp mode, which could explain the bogging......So you have no speedo reading either? As for the clunk, bog and high idle, it could be related to the NSS and VSS being wrong and the IAV is trying to hold the idle up as if you were coasting down the road......

Jay
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Old 12-25-2008, 06:28 PM   #6
qstarin
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Default

Hmm .. well, limp mode would be a problem and would need to be a variable I'd need to get out of the mix.

If no VSS signal kicked the ECU into limp mode, wouldn't I feel that in the car's driveablilty all the time? 99.5% of the time the car drives perfectly like it always has.

And no, my speedo gauge in the dash does not currently operate. I have a good idea what I need to do, but I have to grind some stuff down to fit the sensor and winter is making that hard and the used sensor I got is missing a piece.

I didn't think no VSS signal would cause limp mode - it doesn't even throw a CEL. Of course, now that I think about it - I'll bet my TCU (still hooked up - ABS for the winter) is putting out the appropriate VSS signal for 0mph. lol

So, basically, my car just always thinks it's sitting parked - 0mph & in neutral, except that I'm reving the engine a lot (to drive - lol more).


It never normally bogs at all - and last night it bogged as in no power to accelerate or even hold speed. Dropped into 2nd at 4500 RPM and goosed it and there was no response at all. Hold it down - nothing. Feather it up - nothing.

And it never does it unless I've driven for like 40 min at about 70 (which I only do when going out of town - so far I think its bogged every time since the tranny swap. Funny thing - before the swap, that was about the exact same pattern that would through a P0420 code and I have stock exhaust).



Is there a way I can definitively tell if the car is in or has recently entered limp mode ('01 RS)? Would it always through a CEL or would I definitely be able to feel it?
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Old 12-26-2008, 03:31 PM   #7
Storm
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Very wierd...... If the ECU doesn't know the car is moving, but knows the TPS is closed and the RPM is over the set idle speed, it should close the IACV to drop try and bring the engine speed down. If it can't bring it down, it throws the IAC code. If the car is moving (coasting or decellerating) the ECU will not bring the engine speed all the way down to standing idle speed, as it will anticipate a gear change, accelleration or accept it as normal drive cycle activity. The VSS is the only way the ECU can tell if the car is moving, without this signal, it usually goes into limp mode.

You would definately know when you're in limp mode, as it won't rev past 3500-4000rpm and you may have a flashing CEL at the same time.

Is it possible that you have an intermittent VSS signal somehow? Are you sure you have the NSS and VSS straight and not mixed up?

Jay
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Old 12-26-2008, 04:10 PM   #8
qstarin
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Default

It is weird - I think I'm pretty good at diagnosing things in general, but there's a lot of confounding issues here.

There is no VSS sensor in the car yet. I'm also sure I don't have the VSS & NSS mixed up. I am fairly competent at reading wiring diagrams and wiring, but I don't know cars all that well.

The 4EAT has 2 sensors feeding signals to the TCU. The TCU then spits out the same signal that the VSS in the MT would (goes to the speedo gauge in the dash and the ECU - it's like 4.x pulses per rev or something).

So, my guess is that the TCU, since it's still hooked up, is outputting a 0 mph VSS signal or no signal at all (since there are no sensors cause the 4EAT is not in the car anymore lol). Whatever it is - the car seems to be fine with it.

Definitely not in limp mode normally, the way you describe it - but that could be what the bog was. I do put almost 50 miles a day on my car, and I only experience this issue in these very narrow conditions. For example - the car often is driving and running for the same amount of time but not constantly at 70mph, and it never happens then - only when its 70mph+ steady for that much time.

The NSS wires are currently simply shorted - I can't exactly wire it up directly to the clutch switch because it would kill my remote starter.


I would guess that the ECU is not trying to bring the idle down when driving, cause the TPS would be showing that I'm applying throttle - like just reving it in neutral.

Coasting, though - what you say makes sense - that the TPS would show the pedal up but revs too high. That never seems to be a problem though - like I said, I daily drive this car in the city and it doesn't bog or throw codes (besides the P1596 AT Diagnosis signal high, which I expect). Also, the bog occurs when I'm holding highway speed, so there's some throttle applied (not in cruise).

Last edited by qstarin; 12-26-2008 at 04:27 PM.
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Old 12-26-2008, 08:19 PM   #9
Storm
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Default

By chance, have you tried to run the car without the TCU hooked up? Some of the steps in swapping from 4EAT to 5MT are things I haven't done personally, so I may be overlooking something. It's possible that the 4EAT ECU will let the car run without a VSS directly from the trans.

I'm not sure how much more help I can be....but I will try to contribute if I think of anything else to look at or try.

Jay
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Old 12-26-2008, 10:36 PM   #10
qstarin
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Default

I appreciate the help - its a tricky problem that isn't well suited to forum help. One of those gotta be intimate with the car to really see the whole picture.

I do need to get the TCU out of there. Been trying to wait until summer because I know I will lose ABS until I figure that out (one wire from TCU to ABS, grounding it, 12V & VSS signals to it have all been tried by others and not much success has been reported).

I'll also be putting an i-Speed reflahsed SRS-10 ECU in on Monday - so that'll change things again, potentially.
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Old 12-27-2008, 05:17 PM   #11
qstarin
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Default

So I made the drive home today. 100 miles at 70-80mph (3000-3500 RPM).

It bogged exactly 40 minutes into the drive. Downshifted to 4th right away and it disappeared. That happened 3 more times and downshifting worked each time. None of the bogs were very bad.

It was warmer on the way back. Maybe its something that is worse when its colder.
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Old 04-04-2009, 04:53 AM   #12
dspen666
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Default

i had the same problem. its the idle air control valve. its on top of the throttle body directly in front of the intercooler. you can try to take it off and clean it out with rubbing alcohol, clean in the throttle body where it sits on. you will want to go to the dealer and get a new gasket for it before you take it off though because it will expand. if that doesnt work you, the iacv will have to be replaced. $260. get another gasket just in case. i didnt have to replace the second one because the car was only run for about 20 minutes.

p.s. if you end up replacing the whole thing, take it pretty easy until the car is completely warm, then you can slowly ease into it more. the gasket has to fully seat.

good luck...
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Old 04-04-2009, 12:13 PM   #13
qstarin
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Default

My problem is not the idle air control valve. Thanks for the input, though.
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