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Codes/idle issues


Rom

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Hi all,

So I'm getting the common P1124 and P1126 codes, which pop up about 30-40miles after clearing them. This means the car never gets to emissions readiness either. Idle is a little lumpy, and I've noticed a very slight amount of hesitation at wide open throttle. There is no smoke out the back either. Here's what I have done to try to diagnose this:

1) visual inspection for cracks/pipe issues

2) pulled off oil cap while running. Barely any change in idle and no excess vacuum (so it doesn't appear to be AOS issues).

3) checked the pipe from AOS to intake - no excessive oil so again doesn't appear like an AOS issue.

4) smoked the engine but no leaks appeared.

5) pulled the AOS intake pipe and tried starting. Startup immediately became difficult. With the pipe on startup is never a problem so it seems to confirm the no leak diagnosis.

6) as far as I can tell no cracks in the oil filler pipe. However, I can't be sure as removing the oil cap should have made more of a difference.

7) pulled MAF connector - didn't really change the idle.

Right now I'm thinking maybe a crack I can't see in oil filler or the MAF. I have changed the MAF before about 5 years ago so maybe it's gone again. Would have expected more codes though! Any other ideas on how to diagnose this guys?

Any suggestions appreciated!

Thanks!

Shash

Edited by Rom
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Hi all, So I'm getting the common P1124 and P1126 codes, which pop up about 30-40miles after clearing them. This means the car never gets to emissions readiness either. Idle is a little lumpy, and I've noticed a very slight amount of hesitation at wide open throttle. There is no smoke out the back either. Here's what I have done to try to diagnose this: 1) visual inspection for cracks/pipe issues 2) pulled off oil cap while running. Barely any change in idle and no excess vacuum (so it doesn't appear to be AOS issues). 3) checked the pipe from AOS to intake - no excessive oil so again doesn't appear like an AOS issue. 4) smoked the engine but no leaks appeared. 5) pulled the AOS intake pipe and tried starting. Startup immediately became difficult. With the pipe on startup is never a problem so it seems to confirm the no leak diagnosis. 6) as far as I can tell no cracks in the oil filler pipe. However, I can't be sure as removing the oil cap should have made more of a difference. 7) pulled MAF connector - didn't really change the idle. Right now I'm thinking maybe a crack I can't see in oil filler or the MAF. I have changed the MAF before about 5 years ago so maybe it's gone again. Would have expected more codes though! Any other ideas on how to diagnose this guys? Any suggestions appreciated! Thanks! Shash

Both banks are running so lean the DME cannot richen the mixture further. Normally, most of these are caused by air leaks somewhere in the intake system, but I would check the fuel system for correct pressures and delivery rates. I would also consider having the car's intake area "smoke tested" for small leaks

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Thanks JFP. As mentioned I did do a smoke test and didn't see any leaks. I haven't checked the fuel system yet tho. I also haven't cleaned out the injectors in a while, so that could be part of the issue.

I did notice some oil build up on the top of the intake (where the left/right banks and throttle body meet), as well as on the oil filler pipe inside the engine compartment. I don't have another Boxster to compare to tho. The oil build up is gunky - not wet.

Thanks!

S.

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Hi all,

Just an update.. I think it's crankcase vacuum related. When I remove the oil cap there is no noticeable change in idle, and today I got a vacuum tester on it - the needle didn't even move no matter what I did!

I'm thinking maybe a cracked oil filler pipe, or possibly a failing AOS.

Any other way to categorically determine if it's the AOS? There is no blue smoke and there isn't any excessive oil in the intake-to-AOS pipe.

Thanks!

S.

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Just did a vacuum test on the intake side (pulled off aos pipe and tested there). Strong vacuum (19 inches) and idle seemed to get much better.

Tried to see if the filler pipe was cracked, but doesn't look like it.. at least inside the bay.

Thanks!

S.

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Hi all,

Just an update.. I think it's crankcase vacuum related. When I remove the oil cap there is no noticeable change in idle, and today I got a vacuum tester on it - the needle didn't even move no matter what I did!

I'm thinking maybe a cracked oil filler pipe, or possibly a failing AOS.

Any other way to categorically determine if it's the AOS? There is no blue smoke and there isn't any excessive oil in the intake-to-AOS pipe.

We test AOS units using a fixture we made from an oil filler cap drilled out to accept a barbed hose fitting and a low range inches of water vacuum gauge. A good AOS should show a steady vacuum signal of around 5 inches of water at idle; if it goes over 8-10 (we have seen them come in the shop at over 20), we pull the AOS and replace it.

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Thanks JFP! I measured vacuum at the oil cap and I'm getting close to zero (I know the gauge works fine since I get 19 inches on the intake side), making me believe there is a leak in the crank vacuum, probably in the oil filler pipe under the intake plenum/T-pipe. I'm going to take apart the throttle assembly/T-pipe and see what can be seen.. Need to clean the throttle any way!

Thanks!

S.

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Thanks JFP! I measured vacuum at the oil cap and I'm getting close to zero (I know the gauge works fine since I get 19 inches on the intake side), making me believe there is a leak in the crank vacuum, probably in the oil filler pipe under the intake plenum/T-pipe. I'm going to take apart the throttle assembly/T-pipe and see what can be seen.. Need to clean the throttle any way!

Thanks!

S.

I'd be willing to bet the gauge you measured 19 inches of vacuum on the intake with is measuring in inches of mercury, not water, so I would not be surprised not to see a vacuum signal at the oil cap. Five inches of water would barely move the inches of mercury gauge, and would read about 0.368 inches of mercury.

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I concur what JFP is saying. You need a Manometer that reads in inches of water. This is also a great tool for diagnosing and fixing EVAP systems.

Analog gauge Series 2000 mdl 2030 $63.00

http://www.dwyer-inst.com/Product/Pressure/DifferentialPressure/Gages/Series2000/Ordering

For my digital gauge, mdl 478A-1 $87.00

http://www.dwyer-inst.com/Product/Pressure/Manometers/Digital/Series476A-478A/Ordering

Edited by binger
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Guys, you were right - the gauge was in in/Hg. However:

1) Taking the oil cap off doesn't affect idle at all

2) I believe I can hear a hissing sound from the top of the engine (don't have another Boxster to compare with, but the more I listen to it, the more I think it's not normal

3) Taking the oil cap off seems to change the pitch of the hissing sound very slightly, but not the idle

I think it still points to a leak in the crankcase vacuum system, but I'll do an in/H2O test today with a manometer if I can.

Thanks!

S.

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  • 1 month later...

Hi all,

Finally got some time to work on this! Okay, so here's what I've tried so far:

1) used an in/H2O gauge and it barely registered 1".

2) I took the middle pipe off the oil filler then blocked the plastic pipe going in to the engine (the final part of the filler pipe). Didn't change anything. Still hear the loud-ish hissing, idle still rough.

3) I took the throttle body off and the "T" section linking the intake plenums. There is a fair amount of oil coating the inside in there, although not enough to cause any black/blue smoke at all.

4) I've noticed that everything is covered on the outside with gunk that looks like oil has been building up for a while - on top of the engine, on top of the throttle body, T-piece, etc.

I plan on taking off that final oil filler pipe to see if it's cracked or something. Is that common? Most people I see talk about the middle section (where the accordion bit is). The final piece before the engine seems like solid plastic.

Any other ideas? Help is appreciated!

Thanks!

S.

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Hi all,

Finally got some time to work on this! Okay, so here's what I've tried so far:

1) used an in/H2O gauge and it barely registered 1".

2) I took the middle pipe off the oil filler then blocked the plastic pipe going in to the engine (the final part of the filler pipe). Didn't change anything. Still hear the loud-ish hissing, idle still rough.

3) I took the throttle body off and the "T" section linking the intake plenums. There is a fair amount of oil coating the inside in there, although not enough to cause any black/blue smoke at all.

4) I've noticed that everything is covered on the outside with gunk that looks like oil has been building up for a while - on top of the engine, on top of the throttle body, T-piece, etc.

I plan on taking off that final oil filler pipe to see if it's cracked or something. Is that common? Most people I see talk about the middle section (where the accordion bit is). The final piece before the engine seems like solid plastic.

Any other ideas? Help is appreciated!

Thanks!

S.

The oil fillers do crack in all sections, with the center section failing most often.

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  • 4 weeks later...

Hi all,

Unfortunately I don't get to work on the car often enough (long time between updates!). I finally built a proper smoke machine and was able to smoke the engine out. I can see a lot of smoke coming out near the bottom of the AOS, but can't see anything specific it's coming out of. Note that there has not been any oil smoke out the exhaust, the pressure in the crankcase is extremely low (almost non-existent), and there is barely any oil in the upper AOS-to-throttle-body pipe - which is why I had dismissed the AOS as the issue. However, now I'm thinking maybe a seal around the AOS has failed?

Is there a seal around here that commonly fails and causes all pressure to disappear in the crankcase? I can replace the AOS, but it would be very frustrating to replace the AOS then find that it really isn't that...

Thanks for the help, guys!

S.

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Hi all,

The issue is fixed! It was the bellows, which was badly deteriorated (see below). It ripped up more as I removed it, but it was really gone. I ended up just replacing the entire AOS which came with a new bellow (took about an hour, so wasn't too bad). All issues are resolved, no more codes (after 50 miles driving), and almost all the OBD2 monitors have been set now (just waiting for EVAP and Catalyst to complete).

Thanks all for the help, especially to Ahsai, who hit the nail on the head!

Thanks!

S.

30c3mm0.jpg

Edited by Rom
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