Fuel Trim Malfunction (Bank 1)

[bowjam]

99 Subie Impreza 2.5 RS Auto 70,000 miles

 

My son's car has started idling rough and as low as 500 rpm and surges as high as 2500 rpm with the CEL on.

Codes are PO 304, PO 303, PO 301, PO 170, PO 106 & PO 1143.

I've read most of the threads dealing with the above codes and the Mass Air Flow Sensor seems to be the most logical and number one cause.

I bough this car in January 07 and when I check "My Subaru" records it list the MAF as being replaced in Nov 2006 on a Subaru recall. Could the MAF have gone bad that soon or do I need to look for something else?

It was drivable till I had the codes cleared at Advance Auto. It took me 20 minutes to drive 2 miles home. It was like the engine was out of gasoline but it never died. I spend most of the afternoon working on it.

I changed the fuel filter, air filter, checked for vacuum and exhaust leaks.

Cleaned the MAF with alcohol & Que tips with no noticed improvement.

I would appreciate and welcome any suggestions.

 

Thank You

[porcupine73]

mm...did you check the idle air control valve?

[sea#3]

With the three misfire codes, a fuel trim code and two pressure sensor codes. You might want to check fuel pressure first; if that is OK then I would have a look at your front A/F sensor (02 sensor). They are notorious for going wonky

if the MAF was changed in Nov/06 I doubt it has gone bad. Check to see if it has a blue dot of paint on it (denotes updated part)

 

 

SEA#3

[bowjam]

Thanks for the help Porcupine73 and Sea#3.

Finally warmed up enough here to work outside.

I checked the fuel pressure today and it running about 40-45 psi when I start the engine. However I noticed it's zero with just the ignition on and engina not running.

I was thinking it was an electrical fuel pump ?

 

I haven’t checked the idle air control valve yet..That's next.

Trying to find one to exchange and test without buying a new one.

I will also get around to checking the front A/F sensor (02 sensor)

Once I find out what it looks like and where it is.

The engine is now running so bad that I can’t drive it so hopefully I will find the problem before too long.

 

Thanks again for your help.