Question 2000 Accent MIL P1128 failed emissions. Although I'm sure the actual emissions are fine. How can I be sure it's the MAF sensor? Pcv hose looks fine, bellows appear to be fine. Could a small unnoticed leak in the exhuast cause this? How about fresh spark plugs? Could old spark plugs cause P1128? Once in a while I get a black puff of smoke from the exhaust, when sitting at idle, anything to do with P1128? How do I test the MAF sensor? I may try to get one at the junkyard. If I do fix the problem,how do I shut the MIL off. Disconnect the battery?
AnswerP1128 won't be caused by spark plugs or an exhaust leak. P1128 could put your mixture off, so that could cause black smoke, but I'd primarily expect that on acceleration, not idle.
To test the air flow sensor, you should refer to Hyundai TSB 01-36-022. It gives a chart of engine rpm and throttle position readings and the corresponding air flow readings. The downside is that you'll need a scan tool to read the values, because Hyundai hasn't published a translation between voltage output and the measured air flow that's listed in the TSB.
An air flow sensor wouldn't be one of the parts I would look to purchase from a junk yard. Air flow sensors contaminate easily, and you have little way of knowing what type of environment they have been exposed to. If you choose this route and the problem remains, you'll need to visit the possibility that the sensor you installed was bad as well.
You can reset the MIL by disconnecting the battery. But this will also reset all of the self tests. You'll probably need to drive the car a couple days for the tests to rerun. If you drive a couple days and the lamp hasn't come back on, you may pass the emissions test.
