Any help to avoid breaking the bank. 2015 Mazda 6 GT. Rough idle, almost stalls but doesn’t. Have one code P0172. It could be air or fuel, I don’t know, but I would prefer not to start changing parts for nothing. MAF is clean, spark plugs gapped. In the passed before the code, I may have smelt fuel in the car. Help, please

 

Welcome to the forum

the bread crumbs of a single DTC is not helping you.


There "WILL" be other important information to get in the properly scanning of the ECU with a direct connected to the OBDII diagnostic connector (not any other type blue tooth device like forscan) .
There are at least 3 main area's of the ECU that need to be looked at.

A single DTC never absolutely means that the related part to that DTC or that the DTC was the one activated by the ECU is the direct cause of a issue.

If it were only that easy... LOL

The other concern was the mention of cleaning the MAF. I can't tell you how many we replace each month because they were cleaned by the owner. and damaged it.
As for the spark plugs, we are back to the ECU for more information and unless an *oscilloscope was used to look at the ignition system like spark plugs and coil operation again both DIY and service "mechanics" can and often do without knowing damage either the spark plug or the coil. Also the boots on the coil have multiple parts that if they are not service by replacing them or correctly installing them back on the spark plug can cause engine running issues. One other thing why would you gap the spark plug unless you purchased a copper type plug. most all spark plugs come pre gapped. It is very easy on many special sparks plugs type to *damage the center electrode without knowing your did. Many spark plugs really need special spark plug gapping tools and not the cheap JC Whitey plug gapping tool key chain tool. lol

 

#2 spark plug had a lot of black carbon buildup the other 3 did not

 

Compression test
dry and wet

Then a cylinder leak down test.