I am receiving the P0171 & P0174 error codes. I recently changed the plugs and wires and it has a new air filter.
Runs and idles fine. Checked for vacuum leaks by pulling the the line where it goes into the plenum and it almost stalled out, so I do not think that is the issue. 2001 DII w/ 70,000 miles. Any suggestions are appreciated.

 

P0171 and P0174 means that both banks of your engine are running lean. What kind of air filter did you put in?

 

I got the replacement filter at the dealer as I was there to get a replacement for the hose that connects the radiator to the overflow tank.

 

The maf sensor sounds like a good bet to me but it could also be an air leak somewhere in the intake. I would pressure or vacuum check the intake first for leaks.

 

As long as it is running OK, you have time to figure it out, so don't just start throwing parts at it. The from the air filter box to the t/body for a leak. The air filter box may have a bad seal, bad/broken clips or a crack. Check the o-ring between the iar filter lid and the MAF to make sure it is there and not cracked.
If at some time, you get a tranny code also, like a 733 or 734, then you do have a bad MAF and it will need to be replaced, not cleaned, ASAP.

 

Mike is spot on with this. I had the 171 and 174 codes for a couple of weeks. I then noticed that the truck had difficulty shifting into overdrive. I was deciding on what to do (MAF or O2 sensors) and "not throw money at the truck" when the 734 code popped up.

Read through or search for the post "Ready to buy MAF" by cwood. It helped me immensely, and my truck has run noticeably smoother and with no codes or SES light for 500 miles!

 

Thanks all for the replies, I will look through everything as suggested and go from there.