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CEL not MAF, 1123, 1125, and 1551?!


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I'm a total newbie. '99 Boxster 2.5, 5 speed, 71K miles. I've got a solid CEL with codes 1123, 1125, and 1551. Car runs and idles fine in my opinion. From what I read previously (which has been incredibly education BTW), I thought it might be a bad MAF. Removed and cleaned as prescribed, reset by disconnecting neg terminal on battery - CEL comes backafter 5 miles. So, I unplug the MAF connector, drive 25+ miles, NO CEL and it drives fine. I'm thinking, GREAT, just buy a new MAF and replace. I did this today, brand new MAF from Autohauz - drive 5 miles, CEL is back on.... :angry: I haven't had codes read yet, but what might you think could be the possible options based on the previous codes??? I'll be getting new codes, but wanted to put this out there... Thanks for any help!!

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P1123 Oxygen Sensing Adaptation Area 1 (Cylinders 1 - 3) - Lean Threshold

P1125 Oxygen Sensing Adaptation Area 1 (Cylinders 4 - 6) - Lean Threshold

These codes mean that the DME can not adjust a too rich mixture (it has leaned the mixture as much as possible but can't correct it enough).

PI551 Idle Air Control Valve Closing Coil - Open Circuit

Potential causes:

- Break in wiring.

- IAC valve faulty.

- DME control module faulty

The Idle Air Control Valve sticking could cause a too rich condition that codes say they saw.

I would remove and clean the IAC and make sure it is moving freely. In a few cases the solenoid on the valve fails and it then needs to be replaced.

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Thanks Loren!

So, again, newbie here... On the image here, which is the IAC valve? I've not had to mess with such before and would I clean it with carb cleaner? Any general precautions to take or is it just a straightforward cleaning? Thanks again!

post-24541-1193792842.jpg

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Your diagram is the air injection circuit. IAC is not part of that.

The IAC (item 3) in on the throttle body.

Do not damage of lose the paper gasket item 16.

post-1-1193794955_thumb.png

Yes, sometimes it helps to clean it with carb cleaner. The metal window inside should turn easily.

While you are there I would cleant he throttle body and throttle butterfly too - especially the backside of the throttle butterfly.

As I said in some cases the solenoid fails and the valve then needs to be replaced.

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Thanks again, Loren! You've been a huge help. I'll try it out!

BTW - I knew this site was good when I found the spoiler switch behind the fuse box as suggested here. Turns out, people kick it through frequently. I had NO idea what happened to it until I took the four screws out and looked behind. Small thing, but this place has it all.

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  • 4 months later...

Been a while, but I've cleaned the IACV and throttle body while I was at it. Seems to operate well, although I have codes 1514 and 1551 - all IACV. I don't have ANY issues with idle and all operates normally - very steady idle, no stalling, no problems with RPM's dropping significantly even with AC... other than the annoying CEL. Is there any reason to replace the IACV ($$) if the car runs perfectly well?? Could the codes relate peripherally to something other than a specific IACV issue?

THanks...

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P1514 Idle Air Control Valve Opening Coil - Open Circuit

Possible causes:

- Break in wiring.

- IAC valve faulty.

- DME control module faulty

P1551 Idle Air Control Valve Closing Coil - Open Circuit

Possible causes:

- Break in wiring.

- lAC valve faulty.

- DME control module faulty

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