I recently had a check engine light with restricted performance with codes P0171 & P0174. I did not see any vacuum leaks, so I cleaned the MAF sensor and that seemed to solve the problem...no codes for a few drives totaling 40 or 50 miles. I thought I had solved the problem but today the same codes with restricted performance have come up again. I`m thinking that since the MAF sensor cleaning seemed to work for a short while that maybe it is bad and I may need to replace the MAF sensor. What do all you folks think? I hate to replace the MAF sensor if it is is not bad. Also...is there any downside to buying a reconditioned MAF sensor as opposed to a new one?

 

I have had a reconditioned MAF in my S-type for a couple of years with no issues.

 

My scantool reads fuel pressure at 55 psi. Could this be the problem?

 

I had this problem as well it turned out to be in the accordion folds past the MAF sensor. Almost everyone had a 4 in split in it. I used duck tape until I got to the dealer to purchase one. That solved my issues.

 

Someone on the forum bought a new MAF for really cheap from an outfit in China. I wonder how that turned out...

I bought a reconditioned one a couple of years ago, no problem at all.

 

I changed my fuel filter and those two codes went away.

 

Just remember, 174 and 171 on v8 engines indicates a vacuum leak or loss of air. Usually it has to do with intake gaskets. Most everyone assumes that it is o2 related, but they are doing their job because the computer is indicating lean based on their readings... Save the money on the o2 sensors, and look for leaks.... My two cents..

 

My 03 S Type with V8 not supercharged triggers the lean codes only at idle. Restricted performance light goes off when traveling over 15 or 20 MPH. Egine idle is not affected. No detectable vacum leaks. Do notice the transmission is slow to dwonshift from 2nd to 1st. Is there a vacum line to transmission on the V8? Thought it was all controlled by the PCM. MAF sensor cleaned well, PCV valve replaced. Looking to replace fuel filter, but it is newer with 20 K miles since replacement. Any suggestions?

 

55 psi on OBDII is normal at idle. Be aware that is should maintain about that same pressure throughout the throttle range and under load - give or take a pound or 2. I doubt fuel pressure is an issue, as others indicate here.

 

I'd start with JajJohn's recommendation and look at the air intake tube between the MAFS and Throttle Body. I was getting intermittent restricted performance a few weeks bac and pulled codes - 171 and 174. Was going to clean the MAFS but when I started to remove, I noticed the accordian baffle in the intake tube was cracked on almost every peak. I took this off and the whole bottom was cracked even more - several wraps with duct tape and have been running a week without a restricted performance or any codes and new part on order ($45.00).

Steve

 

Thanks to all for the advice. The problem in my case turned out to be a vacuum hose failure at the fuel pressure regulator. New vacuum elbow solved it!