I had an interesting diagnoses today on the son in law's 2011 Honda Accord, he picked up a set of spark plugs because for one they were due per the mileage and second it had a check engine light and was idling rough. He wanted to do the work himself which I give him credit for, but he asked if I would oversee and give him tips, happy to!
First thing I had him do was pull, make a note of the codes then clear them, it had one code P0171, Lean Bank 1, being a 4 cylinder there is no Bank 2 so it was just a lean condition. From there he changed the plugs, they looked normal so we went to work checking for vacuum leaks. I noticed some seeds and a small knot of pillow stuffing laying in the intake, signs a mouse was trying to make a home so I had him check for chew marks on the wiring and hoses. Not finding anything jumping out at us there I checked the air filter to see if the mouse had made a nest inside the housing, seen that a few times. The air filter was new, no signs of a mouse being in there, he told me he replaced the filter a few months ago, said the old filter wasn't that bad and he didn't see any signs of a mouse then. Not finding anything, now came some contemplation of what to check next. Not having a scanner to watch input and output data it was time to just start visually checking the next most likely culprits so I pulled the Mass Air Flow Sensor, wanted to make sure it wasn't dirty, wasn't expecting to find anything, no codes for it, but son of a gun there was a dead tiny winged bug laying across the beads of the sensors blocking some of the air flow across them. A careful removal of the bug so not to damage the sensors, popped it back in and a test drive and she's good to go. How that bug got in there is anybody's guess, maybe it flew in the air filter housing while he was changing the filter, who knows but that was a first and I was surprised, I really didn't think I'd find anything (visually) wrong with the sensor.
That's diagnosing a problem the old school way, getting in there and checking things without all the fancy do-dad tools. It always comes down to the basics regardless if you use those tools first or not, they do help you eliminate some possibilities but ultimately you have to pull parts and check parts anyways. Had we not found that, after visual checks it would have come down to wiring diagrams, flow charts and checking each input and output with a meter but we got lucky and didn't have to go that far, we were both happy and got the job done quickly. More importantly he learned a few more things today and is gaining more confidence he
can make some repairs himself, of course he can, he just has to loose the fear that he can't. He also got to go home and proudly tell my daughter he fixed it himself.
