John Sampson

I had this code before. I cleaned the MAF and cleared the code and it didn't come back. A few days ago, the idle became erratic and exhibited similar behaviors right before the code was given. I decided to replace the MAF sensor with one I bought last time to be proactive. While driving today my check engine light came on. Same code. My idle bounces a lot between 500-900 RPM, and sometimes almost stalls. My Boxster is a 2002, 2.7 Liter.
Ive included a screenshot of what the OBD2 says. Any suggestions would be great! thanks!

Macster

Reads like an intake air leak.

A pretty bad one given the RPMs are going up and down.

The first time my 2002 2.7l manifested any uneven idle speed behavior proved to be due to an AOS (air oil separator). This was around the 75K mile mark.

If it is the AOS you don't have much time running the engine to "play" around trying to diagnose this before the condition will deteriorate and the engine is at risk of damage from hydraulic lock up as the failing AOS can pull enough oil vapor (possibly even oil droplets) into the intake that this can cause one or more pistons to be unable to continue all the way up the cylinder due to the amount of oil. (The combustion chamber is pretty small, I think around 70cc's which is 2.36 ounces.

When the engine begins smoking that's when the real risk of hydraulic lock up is present.

My advice is to avoid running the engine any. Get the car flat bedded to a shop with techs qualified to work on the car and have the source of the problem id'd and addressed. My Boxster went through 3 AOSs over 15 years and 317K miles. Each one I had replaced at a dealer: One dealer did two of them the local dealer repaired the 3rd one.

John Sampson

Update: I replaced the New MAF with the old one. The idle issue went away. Although this one seems to have slightly less power and runs the car hotter, regardless of how I drive the car. The MPG seems to drop as well, getting 230 miles on a tank vs 380 miles.
The old one is the Bosch MAF, the new one is the Bremi MAF from pelican parts. Bremi gives me weird idle issues, but the car runs better. What should I look at next?

Macster

From my memory of the P1130 (and P1128) error code there is nothing in the documentation regarding the MAF as a possible explanation.

Possible fault causes:

Air intake leak.
Fuel pressure too low.
Fuel injectors contaminated (deposits on tip).
Fuel supply volume too low.

Nothing about a MAF.

There is probably an air intake leak.

I'd recommend you go back to the original MAF assuming it is the correct one for the car/engine. Now the original MAF may be bad (all the time or intermittently) as sometimes there can be two problems but if you suspect the original MAF is bad you can run with the MAF disconnected from the wiring harness and see if this helps. The DME will fuel the engine without the MAF input. Not perfectly but the few times I did this the engine did not react unfavorably to the MAF being disconnected.

The error codes arise when the engine is running too lean at or very close to idle.

Be sure the oil tube cap is on tight and doesn't leak. I found -- albeit after around 150K miles -- the original oil cap was leaking. The leak was "significant" at idle but at higher engine speeds insignificant.

Based on the symptoms/behavior it really reads like an AOS. But you want to a high confidence diagnosis so my advice is get the car in to a shop or smoke test the intake system and find the leak.