Weird idle in neutral and TERRIBLE gas mileage 08

[grammates]

Sorry if it isn’t all correctly worded or not in the right section I’m fairly new
I have an 08 speed 3 with around 75k miles
CAI one cat one test pipe, rmm, HPFP and a tune
Recently my car has been acting very weird and having horrible gas mileage. I had just recently fixed the PCV valve and I keep getting a gross leak code and a too lean at idle code. I’m not too sure why but I continue to get those. Now my car when I’m driving say going 40 and take it out of gear and put it into Neutral and it’s still idling at like 1300-1700 and then won’t really drop too normal rpms until I fully stop. It’s like it’s shifting through the gears on the way down as if it was an auto? Any help would be appreciated I read about it and it said it could be the IAC or a vacuum leak!


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[MSMS3]

Post the exact code numbers, please.

Also can you post a log demonstrating the condition?

Have you done any work on the car recently? Any repairs or changes of parts?

What CAI? What tune?

[Vansquish]

When you're sitting at a stop, does the idle speed bounce around? If so, then you probably have a vacuum leak. Given that you have a few airflow modifications on the car, any one of them *could* be the culprit.

However, I would recommend looking at the last things you touched in the engine bay. If the PCV valve isn't seated properly, or the PCV hose isn't hooked up properly at either the PCV end or the intake manifold, you will have a gross vacuum leak. The car won't run properly, and you will get terrible fuel economy (I did this once, so I'm familiar with the condition).