The car, 2000 Legacy GT with no mods, has recently started to idle rough (like its running on 3 cylinders) when the cold idle starts to slow down. But drove fine, no lack of power, no hesitation and no CEL's. In trying to get rid of the rough idle I changed the air filter, fuel filter, plugs and wires. And it got worse, with added lack of power while driving and sometimes stalling at stop signs. But when it does die it fires right back up and runs fine. Finally got a misfire code for cylinder 1. Brought to a local shop, who tried a new MAP sensor with no change. He also checked fuel pressure and O2 sensors, he said those all checked out fine. But he got a Fuel trim code, I'm guessing the code was for too lean because the old plugs showed signs of running lean. He cleared the code, didn't charge me, but I'm back where I started.
MAF Sensor? Did he put yours back in or did you get to keep the new one? If it wasn't OEM you might not have helped much. My sister picked up a "like OEM" sensor for her bugeye for $200+ and it was crap. She ended up returning it and buying a used one for $40 that worked great. If you still have your original one, have you cleaned it?
Mileage is 176xxx, previous owner said he did timing belt head gaskets and such at 88xxx, so I'm looking forward to doing that again this spring or summer. The shop put my old map back in, the he tried came from napa. maintenance I have done within the last two weeks includes oil change, air and fuel filters and plugs and wires and cleaned the IACV.
My sister's crap-tastic MAF sensor that she returned was a NAPA sensor. She got it brand new, it was 100% crap. I would find someone with an OEM one and try that. You don't even need to buy one. Just find someone with a sensor with the same connector, plug it in and see if that helps. Also have you cleaned yours? A $6 can of cleaner lasts a long time and works wonders.
He hasn't tried a "working" MAF sensor. You can't trust the NAPA ones and we don't know if his is working.... or has been cleaned in 100K miles. It is a good suggestion for ruling things out.
