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The other day while on the way to work the car was running fine. After about 7 miles of highway speeds I exited and stopped at a stop light. When I stopped the engine idle dropped below 500 RPM and started idling very rough. Never had an issue like this before Sunday.

After work it did the same thing as soon as I started the car. On the way back home the CEL came on. I stopped by an Auto Zone and got the following codes:

P0171
P0174
P1131
P1151

All 4 codes mention running lean and suggest something with the MAF. I removed both the MAF and the IAC and cleaned them up. After reinstalling them the problem persists and now the idle will also pulse up and down. It starts off around 1500 RPM, drops to 1000, back up to 1500, then drops to 500 and starts the rough idle again.

I am lost as to what to check next. Any help would be greatly appreciated
 

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^^+1 checking vacuum leaks as that can also lead to a lean condition.

As the upstream O2 sensors provide feedback on the state of the combustion product this may also be a factor even if you are not getting a code specific to the O2 sensor.

How many miles on the car?
 

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If the CEL popped with those 4 codes my first inclination would be to grab a scantool and make sure that you have some type of output from your 02 sensors and MAF. Also check fuel pressure. The 1131 and 1151 codes mean that both 02 sensors are pegged totally lean with no switching, which is unusual to happen suddenly. Could be an 02 sensor wiring short or a massive vacuum leak, as mentioned, by a large vac hose popping off or tearing suddenly.
 
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