Check Engine Light, YAY! (2 codes P0900 P0171)

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im2bad4ya

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MAZDASPEED Protege 2K3.5 #882
I hasn't even been a week since I had this car (a week tomorrow). The guy who sold me the MSP had to change out the alternator, in effect resetting the computer. Well I hit the 75 mile mark and I have the check engine light on with 2 codes:

P0090-Fuel Pressure Regulator 1 Control Circuit
P0171-System Too Lean (Bank 1)

It's not hard to to believe that both codes are related. Probable causes include vacuum leak, dirty MAF or something else. The car drives fine, no erratic idle or anything. So I have to get to the bottom of this issue because I still need to take my car to state inspection. Anyone else have this issue? Do you think simply cleaning the MAF would get rid of both codes? How else can I trouble shoot or know for sure what's causing this?

After searching the forums, it seems P0171 is common? So how can I fix it?

Also in my searches, in regards to P0090, I'm supposed to check the actual connector for the FPR and make sure it's working. I saw a thread that said the ohm reading should be between 22-26 ohms so I'll take a multimeter and check it out.

Anyone run into these issues?
 
try the smallest/free things first. then the cheapest easiest. then if you have to the technical stuff. and yeah the lean is very common. check for some vaccum leaks around the intake mani.
 
My P0171 was caused by a crack in the exhaust manifold. It was leaking enough air to cause the problem. Car also won't hold more than 5psi of boost. Had to replace the manifold. Start by taking off the heat shield and see if you can see any cracks. If there are no visable cracks especially between runners 2 & 3 then pull out the O2 sensor and check for visual damage. You could just need a new O2 sensor which you can pik up at autozone or pepboys.
 
my po171 was a leaking wastegate. which probably has something to do with you only getting 5lbs. i got the atp replacement on and no more code idles/pulls like a boss now
 
fixed itself, I replaced the PRC solenoid from one off a V6 MPV, changed spark plugs, oil, cleaned air filter......code's gone!
 
RETURN OF THE P0171!!! Just came back from the car inspection place (and FINALLY passed inspection) But as I left my check engine light came on. Sure enough I have P0171 again. I don't have any boost issues (9 PSI). I'm not sure what it could be. I'm gonna replace my tranny mount soon so I'll have to pull out the battery and the code will wipe out anyway. But just wanted to see what else could cause the code, I definitely don't want it to come back again.
 
I was having a similar problem on and off for the last 3 months. The light would cycle on and off about once a week. I only had the P0171.
The fix I found (has been 3 weeks and no light has stayed off) was apparently having and aftermarket air filter f's up the MAF sensor.
I cleaned the air filter as well as the MAF. After that the engine light was off immediately. I didn't even have to reset the fuse.
Hope this helps!

EDIT: to further clarify, because the MAF sensor was off, that led to the system running lean. But as everyone else said, the first
thing you should check for is vacuum leaks
 
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