Check Engine Code P2188
 

I bought a used 2008 Mazda3 Hatchback (2.3 L, 5-speed) with about 92,000 miles on it about three weeks ago. For the past two weeks the check engine light has been on. I bought one of those cheap code readers off Amazon and the code came back as P2188 (fuel system too rich at idle). The rpms while idling jump around sporadically from around 500 to maybe 700 rpms and the engine hesitates like its about to shut off. A couple of days ago I went to check the oil level and I noticed the intake has an aftermarket attachment by a company called Simota. I know very little about cars beyond how to change the engine oil and sparkplugs. Do any of you guys have any experience with similar type problems?

Sounds like it needs a good tune up. Is that Simota air filter an oiled type? May have fouled the MAF sensor. You should clean the MAF anyway as it's probably dirty after 92K.

The "hunting idle" is usually a vacuum leak, so look for cracked hoses & the air intake rubber hose could have a crack / leak in it as well. Though i'd think this would cause a too lean fault if anyhing. But 92k miles is enough time to dry some hoses (maybe).
The engine cover on top (plastic) just snaps down into place, pulling that will let you see a few more hoses & such.

Oh, the too rich may be caused by the throttle body being covered in carbon, sealing further than normal & not allowing enough air at idle, which would be the same as fuel too rich. I'm not sure how the idle control works on this, but it is another relatively easy check.

Yup, things to check:
-is the SRI/CAI filter clean, or if reusable oiled?
-is the throttle body clean?
-is the wiring for the MAF sensor intact? (wiggle it and see if it causes a rough idle)
-is the wiring for the MAF under tension? Disconnect it from the battery box