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New CEL Codes

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Ok guys,

I've got some codes for you if you can shed some light on them!

P0102, P1124 and P1126 as previously reported are still there. I have a new MAF on order which I am hoping will nail these. I stripped the intake, cleaned the TB and replaced the AOS over the weekend. While doing this I checked all the hoses I could find, no leaks, but it sure sounds loud around the TB, like rushing air, normal? I've been advised to spray carb cleaner on all the intake and vac hoses by my tech to try and find the leak.

NEW CODES - P0150 (O2 Sensor, maybe related to a failing MAF?), P1551 (IACV make winding) and P1514 (IACV Break Winding) - can anyone shed any light on these.

Engine is rough when cold, better when warm. runs great.

I'd really apreciate any help you can offer chaps!

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Ok, I did a search on the P1551 & P1514 codes and came across a post from 2005..... the last reply was from Loren, sounds like the issue i have as mine is idling rough but runs well warmed up.....

Posted October 22, 2005 - 01:55 PM

Kyrak, on Oct 22 2005, 12:19 PM, said:

Just when you thought it was safe to go back in the Boxster....IT'S BACK! P1514 and P1551 again. Not sure where to go from here. Any advice? ow would i check the coil voltage? Could i have damaged the ICV when cleaning it?


Both of those point to an open idle control valve. Have you checked the voltage to the coil of the valve?

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  • Admin

P1551 Idle Air Control Valve Closing Coil - Open Circuit

Possible causes:

- Break in wiring.

- lAC valve faulty.

- DME control module faulty.

P1514 Idle Air Control Valve Opening Coil - Open Circuit

Possible causes:

- Break in wiring.

- lAC valve faulty.

- DME control module faulty.

Unless your ICV is unplugged or the wiring is broken - you need to replace the ICV.

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Hey thanks for getting back to me Loren. I just checked the ICV wiring harnesses and the wires I could see before they went into the sleeves. They all look fine. Is there anyway I can test the ICV or is it just a case of replacing it?

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Hey thanks for getting back to me Loren. I just checked the ICV wiring harnesses and the wires I could see before they went into the sleeves. They all look fine. Is there anyway I can test the ICV or is it just a case of replacing it?

Check coil resistance of lCV valve.

1. Remove connector of lCV valve.

2. Connect ohmmeter to pins 2 and 3 of lCV valve.

Display: 16 - 19 ohms at 20°C.

If resistance is infinite then it is open (the solenoid is bad).

Not uncommon on older cars.

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Well, i tested the new ICV, resistance 16.9ohms, I also rested the 'old' ICV, resistance also 16.9 ohms. the old one made a buzzing sound with the ignition turned on. Will havr to see how the new one does, waiting for the new MAF before i take it on a test run...... wiring looks ok, hope its not the DME control module on the way out <_<

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  • 1 year later...
  • Admin

Pin 1 and 2 -- 14 to 17 ohms at 20C - (disconnected continuity measurement)

Pin 2 to ground should be infinite ohms - (detect short to ground)

Pin 2 and 3 -- 16 to 19 ohms at 20C - (coil resistance)

I do not see a measurement between pins 1 and 3.

If you have access to a PST2 or PIWIS there is an easy test of the IACV using drive links - activate.

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Thanks Loren, I really do appreciated it.

Sorry yes I have it wrong you are right, I found the correct numbers which match yours from the 986 DME diagnosis manual.

With the IACV disconnected, measuring the IACV itself between pins:

1 & 2 I get 8 ohms (close valve)

2 & 3 I get ~ 16 ohm (open valve)

With engine off, I have Durametric which can activate the IACV and I hear it activating.

On the bench, with a 9v battery, positive to pin 2 and negative to pin 1 the valve closes rapidly and nearly completely. 9v+ to pin 2 and negative to pin 3 and the valve opens rapidly and completely.

I am thinking this might be a marginal IACV... the close valve ohms might be the clue, but there are other clues as well. The idle valve itself does buzz/hum once it gets hot, perhaps because it is leeching voltage due to a failed winding.

Here is what is happening, the hot car is idling along just fine at 680 rpm dead steady without any issue for several minutes and is butter smooth. Then out of the blue just randomly the idle starts to drop to 600, then wander around for a minute or so and then the DME cranks it up to 760ish and it is butter smooth again and then slowly it goes back to 680 where it will idle smooth for a while until the whole stumbling thing happens again.

Here's what the RPM looks like when it is going through one of it's stumbling fits:


I always thought though that the small idle adjustments were done with ignition timing and the large ones with the IACV. Maybe I have that backwards, and what is actually happening is the IACV is not up to the task, so the engine has to compensate with igition timing and explains the idle bouncing around and rough running.

Here are a few more clues, the long term fuel trims are around 1.0, which is normal (car screams at mid-high RPM ranges). But the short term trims near idle crawl back over time, going negative -0.06 currently, and even a little lower if I let the DME learn more (I've seen -0.1), indicating rich running, fuel is not being combusted so it is leaning out the mixture.

Perhaps this is because of lack of air entereing through IACV, the engine is being starved for air (sounds like it too when it's stumbling), and incomplete combustion (sensed by lambda), which is because the DME is closing the idle valve farther than it thinks it is due to the lower than normal "valve close" resistance being 1/2 of what it should be (measured 8 ohms, should be 16 ohms). In other words the DME is closing the valve more than it should, because the resistance is low, and therefore starving the engine of air at idle, incomplete combustion, rough running and eventually less and less fuel to be injected which it thinks will solve the problem.

Does this make sense? I sure hope so, because I can't find any other problems.

Off idle the car runs like a dream.

Dropping $250 on an IACV I don't need to replace seems silly, but ... the evidence is stacking up.

edit: a couple more clues here is that off 680 rpm idle it runs perfect, the stumbling never happens... even something like turning on the high speed fans or more loads, a/c etc. causes the stumbling to never happen.

Edited by logray
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  • 2 weeks later...

Mine is the opposite as yours, Logray. My idle usually starts ~800, slowly climbs to ~1k, then drops back down to ~800.

Testing my IACV at 22.8C, my pins 1-2 show 19.1 ohms.

So, mine may be leaking too much air into the system, where yours wasn't leaking enough?

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  • 2 weeks later...

FRA are both at 1.0, which before the 3.6L injectors was closer to 1.1.

TRA are both just a few hundredths negative, whereas before the new iACV 1 tenth or more neg.

AFR today on the dyno was a very flat 13 ish through the entire RPM range.

Edited by logray
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Good to hear Logray! Glad you got your problem licked.

I wasn't as fortunate. A new IACV did not change anything. My short term trims are still over 0.30. Back to square one.

I ordered a new upper AOS tube and both air intake manifold rubber boots. Those are the last two items that I can replace in the air intake system. Next step will be to go back to the Porsche dealer to have them hook my car up to the smoke machine.

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