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Old 06-25-2016, 03:50 PM   #1
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P1128 & P1130 (Again)

First I did search and found some answers - tried solutions but did not help.
When the car is cold, the engine runs rough for a few minutes then smoothes out.
The p1128 and p1130 codes trigger if the car is in traffic sitting (idle) for an extended period of time.
Car still runs great!
I cleaned the MAF - no difference
I have swapped the MAF - made no difference.
Replaced AOS.
Replaced cracked dip stick tube.
Replaced both pre-cat O2 sensors.
Checked Intake connections - everything is tight.
As per my OBDII Reader, one O2 sensor reads a little higher than the rest.
Any other ideas or suggestions?

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Old 06-25-2016, 05:17 PM   #2
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Which o2 sensor is reading high and is it within range? If not try replacing that sensor (unless already replaced, not clear). You may also try running a bottle of chevron tech Ron through. I did this along with an o2 sensor replacement and my car hasn't popped these codes since.
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Old 06-26-2016, 04:10 AM   #3
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It's not the 02 sensors, they are reading like they should. You have a lean condition caused by false air introduced after the MAF, so not measured by the MAF. The ECU can no longer keep the mixture in range by trimming so throws a code.

1128 and 30 are the idle mixture trim code and not running at speed codes for BOTH sides of the engine. I would concentrate my looking at the center of the plenum for a cracked rubber part of loose clamp. The other thing to change is the fuel pressure regulator on the drivers side of the engine. It's a $45 part and 15 minutes to change.

Chasing these leaks can make you pull your hair out!!!
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Old 06-26-2016, 05:45 AM   #4
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I was reading that "lean" condition on those codes only apply to 98 - 99 cars? On later cars it indicates a "rich" condition? Can anyone confirm this?
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Old 06-26-2016, 07:37 AM   #5
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Ever so slight a vacuum will throw these codes. Check all your hoses including AOS and slip connectors. Mine was the corrugated Aos at TB after 996 conversion.
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Old 06-26-2016, 07:57 AM   #6
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These codes can also come from a dirty or out of spec fuel spray from an injector. The techron can clean them and take care of that. Being that you've taken care of a lot of the primary causes for these codes, try a fuel cleaner.
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Old 06-26-2016, 08:56 AM   #7
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I will give the fuel cleaner a try. Is Techron what most people here are using?
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Old 06-26-2016, 09:09 AM   #8
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I use the Lucas fuel system cleaner. It is also MUCH easier to get into the fuel fill flapper valve without spilling.
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Old 06-26-2016, 09:42 AM   #9
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Quote:
Originally Posted by Boxy_02 View Post
I will give the fuel cleaner a try. Is Techron what most people here are using?
Techron came with the most wide recommendations. Make sure you get the size that treats over 12 gallons.
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Old 06-26-2016, 12:22 PM   #10
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Vacuum leak somewhere. Check the MAF values. For the base it should show 13-15 kg/min. If its less ghan that. You have vacuum leak.
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Old 06-26-2016, 01:48 PM   #11
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Agree an intake air leak is most likely. A failed MAF is also possible as the car is running lean. Clogged injectors are possible but unlikely affecting both banks.

TS guide for 2002 model 986:

DME 7.2 (2000-2002 Boxsters)
P-Code Bank RPM Range Reason Look for:
P1128 1 Idle Engine is running very lean and the fuel adaptation has
pegged its rich correction.
Intake/Exhaust system leaks; MAF not performing correctly; fuel
delivery components cannot deliver enough fuel.
P1130 2 Idle Engine is running very lean and the fuel adaptation has
pegged its rich correction.
Intake/Exhaust system leaks; MAF not performing correctly; fuel
delivery components cannot deliver enough fuel.
P1126 1 Lower Load
(Low RPMs)
Engine is running very lean and the fuel adaptation has
pegged its rich correction.
Intake/Exhaust system leaks; MAF not performing correctly; fuel
delivery components cannot deliver enough fuel.
P1133 2 Lower Load
(Low RPMs)
Engine is running very lean and the fuel adaptation has
pegged its rich correction.
Intake/Exhaust system leaks; MAF not performing correctly; fuel
delivery components cannot deliver enough fuel.
P1125 1 Upper Load
(High RPMs)
Engine is running very lean and the fuel adaptation has
pegged its rich correction.
Intake/Exhaust system leaks; MAF not performing correctly; fuel
delivery components cannot deliver enough fuel.
P1132 2 Upper Load
(High RPMs)
Engine is running very lean and the fuel adaptation has
pegged its rich correction.
Intake/Exhaust system leaks; MAF not performing correctly; fuel
delivery components cannot deliver enough fuel.
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Last edited by Topless; 06-26-2016 at 01:56 PM.
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Old 06-27-2016, 05:42 PM   #12
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This is what I know from hooking up my scan tool (at idle):
1) Both Pre-Cat O2 Sensors fluctuate up and down.
2) Both Post Cat O2 Sensors steady around 0.735
3) MAF reading 3.5-4.0 g/s
4) Pulled Oil Fill Cap, and idle became very bad and there definitely was vacuum present.

The MAF spec above says 13-15 kg/min, should that be kg/hr?
If I do the conversion it is in the ball park 12.6 - 14.4 kg/hr.

Still have not put in the Techron.
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Old 06-28-2016, 06:49 AM   #13
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You may need to smoke the engine to find the leak(s). You can make one easy enough or take it to a shop that has a smoke machine.

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