New Discovery (used) owner here and first time poster , had the vehicle two weeks and its been off the road for a week and a half of that.

Today the engine started a very small misfire under acceleration, it is fine at idle and cruise, just when you hit the gas pedal you can feel it more than hear it. Went to Autozone and had them read the codes, P0171 and P0174. This indicates that the fuel mixture is too lean/rich on both banks, and points to the MAF . It also says it might be an O2 sensor.

Is it possible that the MAF and O2 have gone bad at the same time , or is it safe to guess that it is just the MAF as both banks are showing as rich/weak mixture fault codes? I am going to go ahead and buy the MAF anyway as the vehicle has 167000 miles on it (2000 model), just wondered if I should go ahead and order the O2 sensors at the same time.

Secondly, this just happend a few hours after returning the vehicle to use after waiting for new pullies and tensioner to arrive. Fitted the new tensioner and both the 70 and 90 mm idler pullies in about 10 minutes, then 2 hours trying to figure out how to put the belt on. ( The tensioner pulley actually blew apart).

The vehicle was not misfiring before the pulley broke and snapped the belt, is it possible that it might be linked to the misfire in anyway?

Thanks in advance for any help.

Jim.

 

I would repalce the MAF, reset the codes and then see what comes back, if any.

 

Before you do any more wheeling I would suggest you do a full service on that high miler or you will loose it off road, and it can be a long walk home.
As for the codes, 02's won't cause those codes, a air leak between the air filter box and the t/body can, so will the MAF. Is it getting harder to start, does the exhaust stink, is it having any shifting problems in either 3rd. or 4th gear?